| Message ID | 20191011134358.16912-2-mst@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | vhost: ring format independence | expand |
On 2019/10/11 下午9:45, Michael S. Tsirkin wrote: > The idea is to support multiple ring formats by converting > to a format-independent array of descriptors. > > This costs extra cycles, but we gain in ability > to fetch a batch of descriptors in one go, which > is good for code cache locality. > > To simplify benchmarking, I kept the old code > around so one can switch back and forth by > writing into a module parameter. > This will go away in the final submission. > > This patch causes a minor performance degradation, > it's been kept as simple as possible for ease of review. > Next patch gets us back the performance by adding batching. > > Signed-off-by: Michael S. Tsirkin <mst@redhat.com> > --- > drivers/vhost/test.c | 17 ++- > drivers/vhost/vhost.c | 299 +++++++++++++++++++++++++++++++++++++++++- > drivers/vhost/vhost.h | 16 +++ > 3 files changed, 327 insertions(+), 5 deletions(-) > > diff --git a/drivers/vhost/test.c b/drivers/vhost/test.c > index 056308008288..39a018a7af2d 100644 > --- a/drivers/vhost/test.c > +++ b/drivers/vhost/test.c > @@ -18,6 +18,9 @@ > #include "test.h" > #include "vhost.h" > > +static int newcode = 0; > +module_param(newcode, int, 0644); > + > /* Max number of bytes transferred before requeueing the job. > * Using this limit prevents one virtqueue from starving others. */ > #define VHOST_TEST_WEIGHT 0x80000 > @@ -58,10 +61,16 @@ static void handle_vq(struct vhost_test *n) > vhost_disable_notify(&n->dev, vq); > > for (;;) { > - head = vhost_get_vq_desc(vq, vq->iov, > - ARRAY_SIZE(vq->iov), > - &out, &in, > - NULL, NULL); > + if (newcode) > + head = vhost_get_vq_desc_batch(vq, vq->iov, > + ARRAY_SIZE(vq->iov), > + &out, &in, > + NULL, NULL); > + else > + head = vhost_get_vq_desc(vq, vq->iov, > + ARRAY_SIZE(vq->iov), > + &out, &in, > + NULL, NULL); > /* On error, stop handling until the next kick. */ > if (unlikely(head < 0)) > break; > diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c > index 36ca2cf419bf..36661d6cb51f 100644 > --- a/drivers/vhost/vhost.c > +++ b/drivers/vhost/vhost.c > @@ -301,6 +301,7 @@ static void vhost_vq_reset(struct vhost_dev *dev, > struct vhost_virtqueue *vq) > { > vq->num = 1; > + vq->ndescs = 0; > vq->desc = NULL; > vq->avail = NULL; > vq->used = NULL; > @@ -369,6 +370,9 @@ static int vhost_worker(void *data) > > static void vhost_vq_free_iovecs(struct vhost_virtqueue *vq) > { > + kfree(vq->descs); > + vq->descs = NULL; > + vq->max_descs = 0; > kfree(vq->indirect); > vq->indirect = NULL; > kfree(vq->log); > @@ -385,6 +389,10 @@ static long vhost_dev_alloc_iovecs(struct vhost_dev *dev) > > for (i = 0; i < dev->nvqs; ++i) { > vq = dev->vqs[i]; > + vq->max_descs = dev->iov_limit; > + vq->descs = kmalloc_array(vq->max_descs, > + sizeof(*vq->descs), > + GFP_KERNEL); Is iov_limit too much here? It can obviously increase the footprint. I guess the batching can only be done for descriptor without indirect or next set. Then we may batch 16 or 64. Thanks
On Sat, Oct 12, 2019 at 03:28:49PM +0800, Jason Wang wrote: > > On 2019/10/11 下午9:45, Michael S. Tsirkin wrote: > > The idea is to support multiple ring formats by converting > > to a format-independent array of descriptors. > > > > This costs extra cycles, but we gain in ability > > to fetch a batch of descriptors in one go, which > > is good for code cache locality. > > > > To simplify benchmarking, I kept the old code > > around so one can switch back and forth by > > writing into a module parameter. > > This will go away in the final submission. > > > > This patch causes a minor performance degradation, > > it's been kept as simple as possible for ease of review. > > Next patch gets us back the performance by adding batching. > > > > Signed-off-by: Michael S. Tsirkin <mst@redhat.com> > > --- > > drivers/vhost/test.c | 17 ++- > > drivers/vhost/vhost.c | 299 +++++++++++++++++++++++++++++++++++++++++- > > drivers/vhost/vhost.h | 16 +++ > > 3 files changed, 327 insertions(+), 5 deletions(-) > > > > diff --git a/drivers/vhost/test.c b/drivers/vhost/test.c > > index 056308008288..39a018a7af2d 100644 > > --- a/drivers/vhost/test.c > > +++ b/drivers/vhost/test.c > > @@ -18,6 +18,9 @@ > > #include "test.h" > > #include "vhost.h" > > +static int newcode = 0; > > +module_param(newcode, int, 0644); > > + > > /* Max number of bytes transferred before requeueing the job. > > * Using this limit prevents one virtqueue from starving others. */ > > #define VHOST_TEST_WEIGHT 0x80000 > > @@ -58,10 +61,16 @@ static void handle_vq(struct vhost_test *n) > > vhost_disable_notify(&n->dev, vq); > > for (;;) { > > - head = vhost_get_vq_desc(vq, vq->iov, > > - ARRAY_SIZE(vq->iov), > > - &out, &in, > > - NULL, NULL); > > + if (newcode) > > + head = vhost_get_vq_desc_batch(vq, vq->iov, > > + ARRAY_SIZE(vq->iov), > > + &out, &in, > > + NULL, NULL); > > + else > > + head = vhost_get_vq_desc(vq, vq->iov, > > + ARRAY_SIZE(vq->iov), > > + &out, &in, > > + NULL, NULL); > > /* On error, stop handling until the next kick. */ > > if (unlikely(head < 0)) > > break; > > diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c > > index 36ca2cf419bf..36661d6cb51f 100644 > > --- a/drivers/vhost/vhost.c > > +++ b/drivers/vhost/vhost.c > > @@ -301,6 +301,7 @@ static void vhost_vq_reset(struct vhost_dev *dev, > > struct vhost_virtqueue *vq) > > { > > vq->num = 1; > > + vq->ndescs = 0; > > vq->desc = NULL; > > vq->avail = NULL; > > vq->used = NULL; > > @@ -369,6 +370,9 @@ static int vhost_worker(void *data) > > static void vhost_vq_free_iovecs(struct vhost_virtqueue *vq) > > { > > + kfree(vq->descs); > > + vq->descs = NULL; > > + vq->max_descs = 0; > > kfree(vq->indirect); > > vq->indirect = NULL; > > kfree(vq->log); > > @@ -385,6 +389,10 @@ static long vhost_dev_alloc_iovecs(struct vhost_dev *dev) > > for (i = 0; i < dev->nvqs; ++i) { > > vq = dev->vqs[i]; > > + vq->max_descs = dev->iov_limit; > > + vq->descs = kmalloc_array(vq->max_descs, > > + sizeof(*vq->descs), > > + GFP_KERNEL); > > > Is iov_limit too much here? It can obviously increase the footprint. I guess > the batching can only be done for descriptor without indirect or next set. > Then we may batch 16 or 64. > > Thanks Yes, next patch only batches up to 64. But we do need iov_limit because guest can pass a long chain of scatter/gather. We already have iovecs in a huge array so this does not look like a big deal. If we ever teach the code to avoid the huge iov arrays by handling huge s/g lists piece by piece, we can make the desc array smaller at the same point.
On 2019/10/13 上午4:27, Michael S. Tsirkin wrote: > On Sat, Oct 12, 2019 at 03:28:49PM +0800, Jason Wang wrote: >> On 2019/10/11 下午9:45, Michael S. Tsirkin wrote: >>> The idea is to support multiple ring formats by converting >>> to a format-independent array of descriptors. >>> >>> This costs extra cycles, but we gain in ability >>> to fetch a batch of descriptors in one go, which >>> is good for code cache locality. >>> >>> To simplify benchmarking, I kept the old code >>> around so one can switch back and forth by >>> writing into a module parameter. >>> This will go away in the final submission. >>> >>> This patch causes a minor performance degradation, >>> it's been kept as simple as possible for ease of review. >>> Next patch gets us back the performance by adding batching. >>> >>> Signed-off-by: Michael S. Tsirkin <mst@redhat.com> >>> --- >>> drivers/vhost/test.c | 17 ++- >>> drivers/vhost/vhost.c | 299 +++++++++++++++++++++++++++++++++++++++++- >>> drivers/vhost/vhost.h | 16 +++ >>> 3 files changed, 327 insertions(+), 5 deletions(-) >>> >>> diff --git a/drivers/vhost/test.c b/drivers/vhost/test.c >>> index 056308008288..39a018a7af2d 100644 >>> --- a/drivers/vhost/test.c >>> +++ b/drivers/vhost/test.c >>> @@ -18,6 +18,9 @@ >>> #include "test.h" >>> #include "vhost.h" >>> +static int newcode = 0; >>> +module_param(newcode, int, 0644); >>> + >>> /* Max number of bytes transferred before requeueing the job. >>> * Using this limit prevents one virtqueue from starving others. */ >>> #define VHOST_TEST_WEIGHT 0x80000 >>> @@ -58,10 +61,16 @@ static void handle_vq(struct vhost_test *n) >>> vhost_disable_notify(&n->dev, vq); >>> for (;;) { >>> - head = vhost_get_vq_desc(vq, vq->iov, >>> - ARRAY_SIZE(vq->iov), >>> - &out, &in, >>> - NULL, NULL); >>> + if (newcode) >>> + head = vhost_get_vq_desc_batch(vq, vq->iov, >>> + ARRAY_SIZE(vq->iov), >>> + &out, &in, >>> + NULL, NULL); >>> + else >>> + head = vhost_get_vq_desc(vq, vq->iov, >>> + ARRAY_SIZE(vq->iov), >>> + &out, &in, >>> + NULL, NULL); >>> /* On error, stop handling until the next kick. */ >>> if (unlikely(head < 0)) >>> break; >>> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c >>> index 36ca2cf419bf..36661d6cb51f 100644 >>> --- a/drivers/vhost/vhost.c >>> +++ b/drivers/vhost/vhost.c >>> @@ -301,6 +301,7 @@ static void vhost_vq_reset(struct vhost_dev *dev, >>> struct vhost_virtqueue *vq) >>> { >>> vq->num = 1; >>> + vq->ndescs = 0; >>> vq->desc = NULL; >>> vq->avail = NULL; >>> vq->used = NULL; >>> @@ -369,6 +370,9 @@ static int vhost_worker(void *data) >>> static void vhost_vq_free_iovecs(struct vhost_virtqueue *vq) >>> { >>> + kfree(vq->descs); >>> + vq->descs = NULL; >>> + vq->max_descs = 0; >>> kfree(vq->indirect); >>> vq->indirect = NULL; >>> kfree(vq->log); >>> @@ -385,6 +389,10 @@ static long vhost_dev_alloc_iovecs(struct vhost_dev *dev) >>> for (i = 0; i < dev->nvqs; ++i) { >>> vq = dev->vqs[i]; >>> + vq->max_descs = dev->iov_limit; >>> + vq->descs = kmalloc_array(vq->max_descs, >>> + sizeof(*vq->descs), >>> + GFP_KERNEL); >> >> Is iov_limit too much here? It can obviously increase the footprint. I guess >> the batching can only be done for descriptor without indirect or next set. >> Then we may batch 16 or 64. >> >> Thanks > Yes, next patch only batches up to 64. But we do need iov_limit because > guest can pass a long chain of scatter/gather. > We already have iovecs in a huge array so this does not look like > a big deal. If we ever teach the code to avoid the huge > iov arrays by handling huge s/g lists piece by piece, > we can make the desc array smaller at the same point. > Another possible issue, if we try to batch descriptor chain when we've already batched some descriptors, we may reach the limit then some of the descriptors might need re-read. Or we may need circular index (head, tail) in this case? Thanks
On Mon, Oct 14, 2019 at 09:43:25AM +0800, Jason Wang wrote: > > On 2019/10/13 上午4:27, Michael S. Tsirkin wrote: > > On Sat, Oct 12, 2019 at 03:28:49PM +0800, Jason Wang wrote: > > > On 2019/10/11 下午9:45, Michael S. Tsirkin wrote: > > > > The idea is to support multiple ring formats by converting > > > > to a format-independent array of descriptors. > > > > > > > > This costs extra cycles, but we gain in ability > > > > to fetch a batch of descriptors in one go, which > > > > is good for code cache locality. > > > > > > > > To simplify benchmarking, I kept the old code > > > > around so one can switch back and forth by > > > > writing into a module parameter. > > > > This will go away in the final submission. > > > > > > > > This patch causes a minor performance degradation, > > > > it's been kept as simple as possible for ease of review. > > > > Next patch gets us back the performance by adding batching. > > > > > > > > Signed-off-by: Michael S. Tsirkin <mst@redhat.com> > > > > --- > > > > drivers/vhost/test.c | 17 ++- > > > > drivers/vhost/vhost.c | 299 +++++++++++++++++++++++++++++++++++++++++- > > > > drivers/vhost/vhost.h | 16 +++ > > > > 3 files changed, 327 insertions(+), 5 deletions(-) > > > > > > > > diff --git a/drivers/vhost/test.c b/drivers/vhost/test.c > > > > index 056308008288..39a018a7af2d 100644 > > > > --- a/drivers/vhost/test.c > > > > +++ b/drivers/vhost/test.c > > > > @@ -18,6 +18,9 @@ > > > > #include "test.h" > > > > #include "vhost.h" > > > > +static int newcode = 0; > > > > +module_param(newcode, int, 0644); > > > > + > > > > /* Max number of bytes transferred before requeueing the job. > > > > * Using this limit prevents one virtqueue from starving others. */ > > > > #define VHOST_TEST_WEIGHT 0x80000 > > > > @@ -58,10 +61,16 @@ static void handle_vq(struct vhost_test *n) > > > > vhost_disable_notify(&n->dev, vq); > > > > for (;;) { > > > > - head = vhost_get_vq_desc(vq, vq->iov, > > > > - ARRAY_SIZE(vq->iov), > > > > - &out, &in, > > > > - NULL, NULL); > > > > + if (newcode) > > > > + head = vhost_get_vq_desc_batch(vq, vq->iov, > > > > + ARRAY_SIZE(vq->iov), > > > > + &out, &in, > > > > + NULL, NULL); > > > > + else > > > > + head = vhost_get_vq_desc(vq, vq->iov, > > > > + ARRAY_SIZE(vq->iov), > > > > + &out, &in, > > > > + NULL, NULL); > > > > /* On error, stop handling until the next kick. */ > > > > if (unlikely(head < 0)) > > > > break; > > > > diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c > > > > index 36ca2cf419bf..36661d6cb51f 100644 > > > > --- a/drivers/vhost/vhost.c > > > > +++ b/drivers/vhost/vhost.c > > > > @@ -301,6 +301,7 @@ static void vhost_vq_reset(struct vhost_dev *dev, > > > > struct vhost_virtqueue *vq) > > > > { > > > > vq->num = 1; > > > > + vq->ndescs = 0; > > > > vq->desc = NULL; > > > > vq->avail = NULL; > > > > vq->used = NULL; > > > > @@ -369,6 +370,9 @@ static int vhost_worker(void *data) > > > > static void vhost_vq_free_iovecs(struct vhost_virtqueue *vq) > > > > { > > > > + kfree(vq->descs); > > > > + vq->descs = NULL; > > > > + vq->max_descs = 0; > > > > kfree(vq->indirect); > > > > vq->indirect = NULL; > > > > kfree(vq->log); > > > > @@ -385,6 +389,10 @@ static long vhost_dev_alloc_iovecs(struct vhost_dev *dev) > > > > for (i = 0; i < dev->nvqs; ++i) { > > > > vq = dev->vqs[i]; > > > > + vq->max_descs = dev->iov_limit; > > > > + vq->descs = kmalloc_array(vq->max_descs, > > > > + sizeof(*vq->descs), > > > > + GFP_KERNEL); > > > > > > Is iov_limit too much here? It can obviously increase the footprint. I guess > > > the batching can only be done for descriptor without indirect or next set. > > > Then we may batch 16 or 64. > > > > > > Thanks > > Yes, next patch only batches up to 64. But we do need iov_limit because > > guest can pass a long chain of scatter/gather. > > We already have iovecs in a huge array so this does not look like > > a big deal. If we ever teach the code to avoid the huge > > iov arrays by handling huge s/g lists piece by piece, > > we can make the desc array smaller at the same point. > > > > Another possible issue, if we try to batch descriptor chain when we've > already batched some descriptors, we may reach the limit then some of the > descriptors might need re-read. > > Or we may need circular index (head, tail) in this case? > > Thanks We never supported more than IOV_MAX descriptors. And we don't batch more than iov_limit - IOV_MAX. so buffer never overflows.
On 2019/10/16 上午4:20, Michael S. Tsirkin wrote: > On Mon, Oct 14, 2019 at 09:43:25AM +0800, Jason Wang wrote: >> On 2019/10/13 上午4:27, Michael S. Tsirkin wrote: >>> On Sat, Oct 12, 2019 at 03:28:49PM +0800, Jason Wang wrote: >>>> On 2019/10/11 下午9:45, Michael S. Tsirkin wrote: >>>>> The idea is to support multiple ring formats by converting >>>>> to a format-independent array of descriptors. >>>>> >>>>> This costs extra cycles, but we gain in ability >>>>> to fetch a batch of descriptors in one go, which >>>>> is good for code cache locality. >>>>> >>>>> To simplify benchmarking, I kept the old code >>>>> around so one can switch back and forth by >>>>> writing into a module parameter. >>>>> This will go away in the final submission. >>>>> >>>>> This patch causes a minor performance degradation, >>>>> it's been kept as simple as possible for ease of review. >>>>> Next patch gets us back the performance by adding batching. >>>>> >>>>> Signed-off-by: Michael S. Tsirkin <mst@redhat.com> >>>>> --- >>>>> drivers/vhost/test.c | 17 ++- >>>>> drivers/vhost/vhost.c | 299 +++++++++++++++++++++++++++++++++++++++++- >>>>> drivers/vhost/vhost.h | 16 +++ >>>>> 3 files changed, 327 insertions(+), 5 deletions(-) >>>>> >>>>> diff --git a/drivers/vhost/test.c b/drivers/vhost/test.c >>>>> index 056308008288..39a018a7af2d 100644 >>>>> --- a/drivers/vhost/test.c >>>>> +++ b/drivers/vhost/test.c >>>>> @@ -18,6 +18,9 @@ >>>>> #include "test.h" >>>>> #include "vhost.h" >>>>> +static int newcode = 0; >>>>> +module_param(newcode, int, 0644); >>>>> + >>>>> /* Max number of bytes transferred before requeueing the job. >>>>> * Using this limit prevents one virtqueue from starving others. */ >>>>> #define VHOST_TEST_WEIGHT 0x80000 >>>>> @@ -58,10 +61,16 @@ static void handle_vq(struct vhost_test *n) >>>>> vhost_disable_notify(&n->dev, vq); >>>>> for (;;) { >>>>> - head = vhost_get_vq_desc(vq, vq->iov, >>>>> - ARRAY_SIZE(vq->iov), >>>>> - &out, &in, >>>>> - NULL, NULL); >>>>> + if (newcode) >>>>> + head = vhost_get_vq_desc_batch(vq, vq->iov, >>>>> + ARRAY_SIZE(vq->iov), >>>>> + &out, &in, >>>>> + NULL, NULL); >>>>> + else >>>>> + head = vhost_get_vq_desc(vq, vq->iov, >>>>> + ARRAY_SIZE(vq->iov), >>>>> + &out, &in, >>>>> + NULL, NULL); >>>>> /* On error, stop handling until the next kick. */ >>>>> if (unlikely(head < 0)) >>>>> break; >>>>> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c >>>>> index 36ca2cf419bf..36661d6cb51f 100644 >>>>> --- a/drivers/vhost/vhost.c >>>>> +++ b/drivers/vhost/vhost.c >>>>> @@ -301,6 +301,7 @@ static void vhost_vq_reset(struct vhost_dev *dev, >>>>> struct vhost_virtqueue *vq) >>>>> { >>>>> vq->num = 1; >>>>> + vq->ndescs = 0; >>>>> vq->desc = NULL; >>>>> vq->avail = NULL; >>>>> vq->used = NULL; >>>>> @@ -369,6 +370,9 @@ static int vhost_worker(void *data) >>>>> static void vhost_vq_free_iovecs(struct vhost_virtqueue *vq) >>>>> { >>>>> + kfree(vq->descs); >>>>> + vq->descs = NULL; >>>>> + vq->max_descs = 0; >>>>> kfree(vq->indirect); >>>>> vq->indirect = NULL; >>>>> kfree(vq->log); >>>>> @@ -385,6 +389,10 @@ static long vhost_dev_alloc_iovecs(struct vhost_dev *dev) >>>>> for (i = 0; i < dev->nvqs; ++i) { >>>>> vq = dev->vqs[i]; >>>>> + vq->max_descs = dev->iov_limit; >>>>> + vq->descs = kmalloc_array(vq->max_descs, >>>>> + sizeof(*vq->descs), >>>>> + GFP_KERNEL); >>>> Is iov_limit too much here? It can obviously increase the footprint. I guess >>>> the batching can only be done for descriptor without indirect or next set. >>>> Then we may batch 16 or 64. >>>> >>>> Thanks >>> Yes, next patch only batches up to 64. But we do need iov_limit because >>> guest can pass a long chain of scatter/gather. >>> We already have iovecs in a huge array so this does not look like >>> a big deal. If we ever teach the code to avoid the huge >>> iov arrays by handling huge s/g lists piece by piece, >>> we can make the desc array smaller at the same point. >>> >> Another possible issue, if we try to batch descriptor chain when we've >> already batched some descriptors, we may reach the limit then some of the >> descriptors might need re-read. >> >> Or we may need circular index (head, tail) in this case? >> >> Thanks > We never supported more than IOV_MAX descriptors. > And we don't batch more than iov_limit - IOV_MAX. Ok, but what happens when we've already batched 63 descriptors then come a 3 descriptor chain? And it looks to me we need forget the cached descriptor during set_vring_base() Thanks > > so buffer never overflows. >
diff --git a/drivers/vhost/test.c b/drivers/vhost/test.c index 056308008288..39a018a7af2d 100644 --- a/drivers/vhost/test.c +++ b/drivers/vhost/test.c @@ -18,6 +18,9 @@ #include "test.h" #include "vhost.h" +static int newcode = 0; +module_param(newcode, int, 0644); + /* Max number of bytes transferred before requeueing the job. * Using this limit prevents one virtqueue from starving others. */ #define VHOST_TEST_WEIGHT 0x80000 @@ -58,10 +61,16 @@ static void handle_vq(struct vhost_test *n) vhost_disable_notify(&n->dev, vq); for (;;) { - head = vhost_get_vq_desc(vq, vq->iov, - ARRAY_SIZE(vq->iov), - &out, &in, - NULL, NULL); + if (newcode) + head = vhost_get_vq_desc_batch(vq, vq->iov, + ARRAY_SIZE(vq->iov), + &out, &in, + NULL, NULL); + else + head = vhost_get_vq_desc(vq, vq->iov, + ARRAY_SIZE(vq->iov), + &out, &in, + NULL, NULL); /* On error, stop handling until the next kick. */ if (unlikely(head < 0)) break; diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c index 36ca2cf419bf..36661d6cb51f 100644 --- a/drivers/vhost/vhost.c +++ b/drivers/vhost/vhost.c @@ -301,6 +301,7 @@ static void vhost_vq_reset(struct vhost_dev *dev, struct vhost_virtqueue *vq) { vq->num = 1; + vq->ndescs = 0; vq->desc = NULL; vq->avail = NULL; vq->used = NULL; @@ -369,6 +370,9 @@ static int vhost_worker(void *data) static void vhost_vq_free_iovecs(struct vhost_virtqueue *vq) { + kfree(vq->descs); + vq->descs = NULL; + vq->max_descs = 0; kfree(vq->indirect); vq->indirect = NULL; kfree(vq->log); @@ -385,6 +389,10 @@ static long vhost_dev_alloc_iovecs(struct vhost_dev *dev) for (i = 0; i < dev->nvqs; ++i) { vq = dev->vqs[i]; + vq->max_descs = dev->iov_limit; + vq->descs = kmalloc_array(vq->max_descs, + sizeof(*vq->descs), + GFP_KERNEL); vq->indirect = kmalloc_array(UIO_MAXIOV, sizeof(*vq->indirect), GFP_KERNEL); @@ -392,7 +400,7 @@ static long vhost_dev_alloc_iovecs(struct vhost_dev *dev) GFP_KERNEL); vq->heads = kmalloc_array(dev->iov_limit, sizeof(*vq->heads), GFP_KERNEL); - if (!vq->indirect || !vq->log || !vq->heads) + if (!vq->indirect || !vq->log || !vq->heads || !vq->descs) goto err_nomem; } return 0; @@ -2346,6 +2354,295 @@ int vhost_get_vq_desc(struct vhost_virtqueue *vq, } EXPORT_SYMBOL_GPL(vhost_get_vq_desc); +static struct vhost_desc *peek_split_desc(struct vhost_virtqueue *vq) +{ + BUG_ON(!vq->ndescs); + return &vq->descs[vq->ndescs - 1]; +} + +static void pop_split_desc(struct vhost_virtqueue *vq) +{ + BUG_ON(!vq->ndescs); + --vq->ndescs; +} + +static int push_split_desc(struct vhost_virtqueue *vq, struct vring_desc *desc, u16 id) +{ + struct vhost_desc *h; + + if (unlikely(vq->ndescs >= vq->max_descs)) + return -EINVAL; + h = &vq->descs[vq->ndescs++]; + h->addr = vhost64_to_cpu(vq, desc->addr); + h->len = vhost32_to_cpu(vq, desc->len); + h->flags = vhost16_to_cpu(vq, desc->flags); + h->id = id; + + return 0; +} + +static int fetch_indirect_descs(struct vhost_virtqueue *vq, + struct vhost_desc *indirect, + u16 head) +{ + struct vring_desc desc; + unsigned int i = 0, count, found = 0; + u32 len = indirect->len; + struct iov_iter from; + int ret; + + /* Sanity check */ + if (unlikely(len % sizeof desc)) { + vq_err(vq, "Invalid length in indirect descriptor: " + "len 0x%llx not multiple of 0x%zx\n", + (unsigned long long)len, + sizeof desc); + return -EINVAL; + } + + ret = translate_desc(vq, indirect->addr, len, vq->indirect, + UIO_MAXIOV, VHOST_ACCESS_RO); + if (unlikely(ret < 0)) { + if (ret != -EAGAIN) + vq_err(vq, "Translation failure %d in indirect.\n", ret); + return ret; + } + iov_iter_init(&from, READ, vq->indirect, ret, len); + + /* We will use the result as an address to read from, so most + * architectures only need a compiler barrier here. */ + read_barrier_depends(); + + count = len / sizeof desc; + /* Buffers are chained via a 16 bit next field, so + * we can have at most 2^16 of these. */ + if (unlikely(count > USHRT_MAX + 1)) { + vq_err(vq, "Indirect buffer length too big: %d\n", + indirect->len); + return -E2BIG; + } + if (unlikely(vq->ndescs + count > vq->max_descs)) { + vq_err(vq, "Too many indirect + direct descs: %d + %d\n", + vq->ndescs, indirect->len); + return -E2BIG; + } + + do { + if (unlikely(++found > count)) { + vq_err(vq, "Loop detected: last one at %u " + "indirect size %u\n", + i, count); + return -EINVAL; + } + if (unlikely(!copy_from_iter_full(&desc, sizeof(desc), &from))) { + vq_err(vq, "Failed indirect descriptor: idx %d, %zx\n", + i, (size_t)indirect->addr + i * sizeof desc); + return -EINVAL; + } + if (unlikely(desc.flags & cpu_to_vhost16(vq, VRING_DESC_F_INDIRECT))) { + vq_err(vq, "Nested indirect descriptor: idx %d, %zx\n", + i, (size_t)indirect->addr + i * sizeof desc); + return -EINVAL; + } + + push_split_desc(vq, &desc, head); + } while ((i = next_desc(vq, &desc)) != -1); + return 0; +} + +static int fetch_descs(struct vhost_virtqueue *vq) +{ + struct vring_desc desc; + unsigned int i, head, found = 0; + u16 last_avail_idx; + __virtio16 avail_idx; + __virtio16 ring_head; + int ret; + + /* Check it isn't doing very strange things with descriptor numbers. */ + last_avail_idx = vq->last_avail_idx; + + if (vq->avail_idx == vq->last_avail_idx) { + if (unlikely(vhost_get_avail_idx(vq, &avail_idx))) { + vq_err(vq, "Failed to access avail idx at %p\n", + &vq->avail->idx); + return -EFAULT; + } + vq->avail_idx = vhost16_to_cpu(vq, avail_idx); + + if (unlikely((u16)(vq->avail_idx - last_avail_idx) > vq->num)) { + vq_err(vq, "Guest moved used index from %u to %u", + last_avail_idx, vq->avail_idx); + return -EFAULT; + } + + /* If there's nothing new since last we looked, return + * invalid. + */ + if (vq->avail_idx == last_avail_idx) + return vq->num; + + /* Only get avail ring entries after they have been + * exposed by guest. + */ + smp_rmb(); + } + + /* Grab the next descriptor number they're advertising */ + if (unlikely(vhost_get_avail_head(vq, &ring_head, last_avail_idx))) { + vq_err(vq, "Failed to read head: idx %d address %p\n", + last_avail_idx, + &vq->avail->ring[last_avail_idx % vq->num]); + return -EFAULT; + } + + head = vhost16_to_cpu(vq, ring_head); + + /* If their number is silly, that's an error. */ + if (unlikely(head >= vq->num)) { + vq_err(vq, "Guest says index %u > %u is available", + head, vq->num); + return -EINVAL; + } + + i = head; + do { + if (unlikely(i >= vq->num)) { + vq_err(vq, "Desc index is %u > %u, head = %u", + i, vq->num, head); + return -EINVAL; + } + if (unlikely(++found > vq->num)) { + vq_err(vq, "Loop detected: last one at %u " + "vq size %u head %u\n", + i, vq->num, head); + return -EINVAL; + } + ret = vhost_get_desc(vq, &desc, i); + if (unlikely(ret)) { + vq_err(vq, "Failed to get descriptor: idx %d addr %p\n", + i, vq->desc + i); + return -EFAULT; + } + ret = push_split_desc(vq, &desc, head); + if (unlikely(ret)) { + vq_err(vq, "Failed to save descriptor: idx %d\n", i); + return -EINVAL; + } + } while ((i = next_desc(vq, &desc)) != -1); + + /* On success, increment avail index. */ + vq->last_avail_idx++; + + /* Assume notifications from guest are disabled at this point, + * if they aren't we would need to update avail_event index. */ + BUG_ON(!(vq->used_flags & VRING_USED_F_NO_NOTIFY)); + + return 0; +} + +/* This looks in the virtqueue and for the first available buffer, and converts + * it to an iovec for convenient access. Since descriptors consist of some + * number of output then some number of input descriptors, it's actually two + * iovecs, but we pack them into one and note how many of each there were. + * + * This function returns the descriptor number found, or vq->num (which is + * never a valid descriptor number) if none was found. A negative code is + * returned on error. */ +int vhost_get_vq_desc_batch(struct vhost_virtqueue *vq, + struct iovec iov[], unsigned int iov_size, + unsigned int *out_num, unsigned int *in_num, + struct vhost_log *log, unsigned int *log_num) +{ + int ret = fetch_descs(vq); + struct vhost_desc *last; + u16 id; + int i; + + if (ret) + return ret; + + last = peek_split_desc(vq); + id = last->id; + + if (last->flags & VRING_DESC_F_INDIRECT) { + int r; + + pop_split_desc(vq); + r = fetch_indirect_descs(vq, last, id); + if (unlikely(r < 0)) { + if (r != -EAGAIN) + vq_err(vq, "Failure detected " + "in indirect descriptor at idx %d\n", id); + return ret; + } + } + + /* Now convert to IOV */ + /* When we start there are none of either input nor output. */ + *out_num = *in_num = 0; + if (unlikely(log)) + *log_num = 0; + + for (i = 0; i < vq->ndescs; ++i) { + unsigned iov_count = *in_num + *out_num; + struct vhost_desc *desc = &vq->descs[i]; + int access; + + if (desc->flags & ~(VRING_DESC_F_INDIRECT | VRING_DESC_F_WRITE)) { + vq_err(vq, "Unexpected flags: 0x%x at descriptor id 0x%x\n", + desc->flags, desc->id); + ret = -EINVAL; + goto err; + } + if (desc->flags & VRING_DESC_F_WRITE) + access = VHOST_ACCESS_WO; + else + access = VHOST_ACCESS_RO; + ret = translate_desc(vq, desc->addr, + desc->len, iov + iov_count, + iov_size - iov_count, access); + if (unlikely(ret < 0)) { + if (ret != -EAGAIN) + vq_err(vq, "Translation failure %d descriptor idx %d\n", + ret, i); + goto err; + } + if (access == VHOST_ACCESS_WO) { + /* If this is an input descriptor, + * increment that count. */ + *in_num += ret; + if (unlikely(log && ret)) { + log[*log_num].addr = desc->addr; + log[*log_num].len = desc->len; + ++*log_num; + } + } else { + /* If it's an output descriptor, they're all supposed + * to come before any input descriptors. */ + if (unlikely(*in_num)) { + vq_err(vq, "Descriptor has out after in: " + "idx %d\n", i); + ret = -EINVAL; + goto err; + } + *out_num += ret; + } + } + + ret = id; + vq->ndescs = 0; + + return ret; + +err: + vhost_discard_vq_desc(vq, 1); + vq->ndescs = 0; + + return ret; +} +EXPORT_SYMBOL_GPL(vhost_get_vq_desc_batch); + /* Reverse the effect of vhost_get_vq_desc. Useful for error handling. */ void vhost_discard_vq_desc(struct vhost_virtqueue *vq, int n) { diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h index e9ed2722b633..1724f61b6c2d 100644 --- a/drivers/vhost/vhost.h +++ b/drivers/vhost/vhost.h @@ -80,6 +80,13 @@ enum vhost_uaddr_type { VHOST_NUM_ADDRS = 3, }; +struct vhost_desc { + u64 addr; + u32 len; + u16 flags; /* VRING_DESC_F_WRITE, VRING_DESC_F_NEXT */ + u16 id; +}; + /* The virtqueue structure describes a queue attached to a device. */ struct vhost_virtqueue { struct vhost_dev *dev; @@ -90,6 +97,11 @@ struct vhost_virtqueue { struct vring_desc __user *desc; struct vring_avail __user *avail; struct vring_used __user *used; + + struct vhost_desc *descs; + int ndescs; + int max_descs; + const struct vhost_umem_node *meta_iotlb[VHOST_NUM_ADDRS]; struct file *kick; struct eventfd_ctx *call_ctx; @@ -190,6 +202,10 @@ long vhost_vring_ioctl(struct vhost_dev *d, unsigned int ioctl, void __user *arg bool vhost_vq_access_ok(struct vhost_virtqueue *vq); bool vhost_log_access_ok(struct vhost_dev *); +int vhost_get_vq_desc_batch(struct vhost_virtqueue *, + struct iovec iov[], unsigned int iov_count, + unsigned int *out_num, unsigned int *in_num, + struct vhost_log *log, unsigned int *log_num); int vhost_get_vq_desc(struct vhost_virtqueue *, struct iovec iov[], unsigned int iov_count, unsigned int *out_num, unsigned int *in_num,
The idea is to support multiple ring formats by converting to a format-independent array of descriptors. This costs extra cycles, but we gain in ability to fetch a batch of descriptors in one go, which is good for code cache locality. To simplify benchmarking, I kept the old code around so one can switch back and forth by writing into a module parameter. This will go away in the final submission. This patch causes a minor performance degradation, it's been kept as simple as possible for ease of review. Next patch gets us back the performance by adding batching. Signed-off-by: Michael S. Tsirkin <mst@redhat.com> --- drivers/vhost/test.c | 17 ++- drivers/vhost/vhost.c | 299 +++++++++++++++++++++++++++++++++++++++++- drivers/vhost/vhost.h | 16 +++ 3 files changed, 327 insertions(+), 5 deletions(-)