| Message ID | 20210729073503.187-2-xieyongji@bytedance.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Introduce VDUSE - vDPA Device in Userspace | expand |
在 2021/7/29 下午3:34, Xie Yongji 写道: > Export alloc_iova_fast() and free_iova_fast() so that > some modules can use it to improve iova allocation efficiency. It's better to explain which alloc_iova() is not sufficient here. Thanks > > Signed-off-by: Xie Yongji <xieyongji@bytedance.com> > --- > drivers/iommu/iova.c | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/drivers/iommu/iova.c b/drivers/iommu/iova.c > index b6cf5f16123b..3941ed6bb99b 100644 > --- a/drivers/iommu/iova.c > +++ b/drivers/iommu/iova.c > @@ -521,6 +521,7 @@ alloc_iova_fast(struct iova_domain *iovad, unsigned long size, > > return new_iova->pfn_lo; > } > +EXPORT_SYMBOL_GPL(alloc_iova_fast); > > /** > * free_iova_fast - free iova pfn range into rcache > @@ -538,6 +539,7 @@ free_iova_fast(struct iova_domain *iovad, unsigned long pfn, unsigned long size) > > free_iova(iovad, pfn); > } > +EXPORT_SYMBOL_GPL(free_iova_fast); > > #define fq_ring_for_each(i, fq) \ > for ((i) = (fq)->head; (i) != (fq)->tail; (i) = ((i) + 1) % IOVA_FQ_SIZE)
在 2021/7/29 下午3:34, Xie Yongji 写道: > Export alloc_iova_fast() and free_iova_fast() so that > some modules can use it to improve iova allocation efficiency. It's better to explain why alloc_iova() is not sufficient here. Thanks > > Signed-off-by: Xie Yongji <xieyongji@bytedance.com> > --- > drivers/iommu/iova.c | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/drivers/iommu/iova.c b/drivers/iommu/iova.c > index b6cf5f16123b..3941ed6bb99b 100644 > --- a/drivers/iommu/iova.c > +++ b/drivers/iommu/iova.c > @@ -521,6 +521,7 @@ alloc_iova_fast(struct iova_domain *iovad, unsigned long size, > > return new_iova->pfn_lo; > } > +EXPORT_SYMBOL_GPL(alloc_iova_fast); > > /** > * free_iova_fast - free iova pfn range into rcache > @@ -538,6 +539,7 @@ free_iova_fast(struct iova_domain *iovad, unsigned long pfn, unsigned long size) > > free_iova(iovad, pfn); > } > +EXPORT_SYMBOL_GPL(free_iova_fast); > > #define fq_ring_for_each(i, fq) \ > for ((i) = (fq)->head; (i) != (fq)->tail; (i) = ((i) + 1) % IOVA_FQ_SIZE)
On Tue, Aug 3, 2021 at 3:41 PM Jason Wang <jasowang@redhat.com> wrote: > > > 在 2021/7/29 下午3:34, Xie Yongji 写道: > > Export alloc_iova_fast() and free_iova_fast() so that > > some modules can use it to improve iova allocation efficiency. > > > It's better to explain why alloc_iova() is not sufficient here. > Fine. Thanks, Yongji
On 2021-08-03 09:54, Yongji Xie wrote: > On Tue, Aug 3, 2021 at 3:41 PM Jason Wang <jasowang@redhat.com> wrote: >> >> >> 在 2021/7/29 下午3:34, Xie Yongji 写道: >>> Export alloc_iova_fast() and free_iova_fast() so that >>> some modules can use it to improve iova allocation efficiency. >> >> >> It's better to explain why alloc_iova() is not sufficient here. >> > > Fine. What I fail to understand from the later patches is what the IOVA domain actually represents. If the "device" is a userspace process then logically the "IOVA" would be the userspace address, so presumably somewhere you're having to translate between this arbitrary address space and actual usable addresses - if you're worried about efficiency surely it would be even better to not do that? Presumably userspace doesn't have any concern about alignment and the things we have to worry about for the DMA API in general, so it's pretty much just allocating slots in a buffer, and there are far more effective ways to do that than a full-blown address space manager. If you're going to reuse any infrastructure I'd have expected it to be SWIOTLB rather than the IOVA allocator. Because, y'know, you're *literally implementing a software I/O TLB* ;) Robin.
On Tue, Aug 3, 2021 at 6:54 PM Robin Murphy <robin.murphy@arm.com> wrote: > > On 2021-08-03 09:54, Yongji Xie wrote: > > On Tue, Aug 3, 2021 at 3:41 PM Jason Wang <jasowang@redhat.com> wrote: > >> > >> > >> 在 2021/7/29 下午3:34, Xie Yongji 写道: > >>> Export alloc_iova_fast() and free_iova_fast() so that > >>> some modules can use it to improve iova allocation efficiency. > >> > >> > >> It's better to explain why alloc_iova() is not sufficient here. > >> > > > > Fine. > > What I fail to understand from the later patches is what the IOVA domain > actually represents. If the "device" is a userspace process then > logically the "IOVA" would be the userspace address, so presumably > somewhere you're having to translate between this arbitrary address > space and actual usable addresses - if you're worried about efficiency > surely it would be even better to not do that? > Yes, userspace daemon needs to translate the "IOVA" in a DMA descriptor to the VA (from mmap(2)). But this actually doesn't affect performance since it's an identical mapping in most cases. > Presumably userspace doesn't have any concern about alignment and the > things we have to worry about for the DMA API in general, so it's pretty > much just allocating slots in a buffer, and there are far more effective > ways to do that than a full-blown address space manager. Considering iova allocation efficiency, I think the iova allocator is better here. In most cases, we don't even need to hold a spin lock during iova allocation. > If you're going > to reuse any infrastructure I'd have expected it to be SWIOTLB rather > than the IOVA allocator. Because, y'know, you're *literally implementing > a software I/O TLB* ;) > But actually what we can reuse in SWIOTLB is the IOVA allocator. And the IOVA management in SWIOTLB is not what we want. For example, SWIOTLB allocates and uses contiguous memory for bouncing, which is not necessary in VDUSE case. And VDUSE needs coherent mapping which is not supported by the SWIOTLB. Besides, the SWIOTLB works in singleton mode (designed for platform IOMMU) , but VDUSE is based on on-chip IOMMU (supports multiple instances). So I still prefer to reuse the IOVA allocator to implement a MMU-based software IOTLB. Thanks, Yongji
On 2021-08-04 06:02, Yongji Xie wrote: > On Tue, Aug 3, 2021 at 6:54 PM Robin Murphy <robin.murphy@arm.com> wrote: >> >> On 2021-08-03 09:54, Yongji Xie wrote: >>> On Tue, Aug 3, 2021 at 3:41 PM Jason Wang <jasowang@redhat.com> wrote: >>>> >>>> >>>> 在 2021/7/29 下午3:34, Xie Yongji 写道: >>>>> Export alloc_iova_fast() and free_iova_fast() so that >>>>> some modules can use it to improve iova allocation efficiency. >>>> >>>> >>>> It's better to explain why alloc_iova() is not sufficient here. >>>> >>> >>> Fine. >> >> What I fail to understand from the later patches is what the IOVA domain >> actually represents. If the "device" is a userspace process then >> logically the "IOVA" would be the userspace address, so presumably >> somewhere you're having to translate between this arbitrary address >> space and actual usable addresses - if you're worried about efficiency >> surely it would be even better to not do that? >> > > Yes, userspace daemon needs to translate the "IOVA" in a DMA > descriptor to the VA (from mmap(2)). But this actually doesn't affect > performance since it's an identical mapping in most cases. I'm not familiar with the vhost_iotlb stuff, but it looks suspiciously like you're walking yet another tree to make those translations. Even if the buffer can be mapped all at once with a fixed offset such that each DMA mapping call doesn't need a lookup for each individual "IOVA" - that might be what's happening already, but it's a bit hard to follow just reading the patches in my mail client - vhost_iotlb_add_range() doesn't look like it's super-cheap to call, and you're serialising on a lock for that. My main point, though, is that if you've already got something else keeping track of the actual addresses, then the way you're using an iova_domain appears to be something you could do with a trivial bitmap allocator. That's why I don't buy the efficiency argument. The main design points of the IOVA allocator are to manage large address spaces while trying to maximise spatial locality to minimise the underlying pagetable usage, and allocating with a flexible limit to support multiple devices with different addressing capabilities in the same address space. If none of those aspects are relevant to the use-case - which AFAICS appears to be true here - then as a general-purpose resource allocator it's rubbish and has an unreasonably massive memory overhead and there are many, many better choices. FWIW I've recently started thinking about moving all the caching stuff out of iova_domain and into the iommu-dma layer since it's now a giant waste of space for all the other current IOVA users. >> Presumably userspace doesn't have any concern about alignment and the >> things we have to worry about for the DMA API in general, so it's pretty >> much just allocating slots in a buffer, and there are far more effective >> ways to do that than a full-blown address space manager. > > Considering iova allocation efficiency, I think the iova allocator is > better here. In most cases, we don't even need to hold a spin lock > during iova allocation. > >> If you're going >> to reuse any infrastructure I'd have expected it to be SWIOTLB rather >> than the IOVA allocator. Because, y'know, you're *literally implementing >> a software I/O TLB* ;) >> > > But actually what we can reuse in SWIOTLB is the IOVA allocator. Huh? Those are completely unrelated and orthogonal things - SWIOTLB does not use an external allocator (see find_slots()). By SWIOTLB I mean specifically the library itself, not dma-direct or any of the other users built around it. The functionality for managing slots in a buffer and bouncing data in and out can absolutely be reused - that's why users like the Xen and iommu-dma code *are* reusing it instead of open-coding their own versions. > And > the IOVA management in SWIOTLB is not what we want. For example, > SWIOTLB allocates and uses contiguous memory for bouncing, which is > not necessary in VDUSE case. alloc_iova() allocates a contiguous (in IOVA address) region of space. In vduse_domain_map_page() you use it to allocate a contiguous region of space from your bounce buffer. Can you clarify how that is fundamentally different from allocating a contiguous region of space from a bounce buffer? Nobody's saying the underlying implementation details of where the buffer itself comes from can't be tweaked. > And VDUSE needs coherent mapping which is > not supported by the SWIOTLB. Besides, the SWIOTLB works in singleton > mode (designed for platform IOMMU) , but VDUSE is based on on-chip > IOMMU (supports multiple instances). That's not entirely true - the IOMMU bounce buffering scheme introduced in intel-iommu and now moved into the iommu-dma layer was already a step towards something conceptually similar. It does still rely on stealing the underlying pages from the global SWIOTLB pool at the moment, but the bouncing is effectively done in a per-IOMMU-domain context. The next step is currently queued in linux-next, wherein we can now have individual per-device SWIOTLB pools. In fact at that point I think you might actually be able to do your thing without implementing any special DMA ops at all - you'd need to set up a pool for your "device" with force_bounce set, then when you mmap() that to userspace, set up dev->dma_range_map to describe an offset from the physical address of the buffer to the userspace address, and I think dma-direct would be tricked into doing the right thing. It's a bit wacky, but it could stand to save a hell of a lot of bother. Finally, enhancing SWIOTLB to cope with virtually-mapped buffers that don't have to be physically contiguous is a future improvement which I think could benefit various use-cases - indeed it's possibly already on the table for IOMMU bounce pages - so would probably be welcome in general. > So I still prefer to reuse the > IOVA allocator to implement a MMU-based software IOTLB. If you're dead set on open-coding all the bounce-buffering machinery, then I'd honestly recommend open-coding a more suitable buffer allocator as well ;) Thanks, Robin.
On Wed, Aug 4, 2021 at 11:43 PM Robin Murphy <robin.murphy@arm.com> wrote: > > On 2021-08-04 06:02, Yongji Xie wrote: > > On Tue, Aug 3, 2021 at 6:54 PM Robin Murphy <robin.murphy@arm.com> wrote: > >> > >> On 2021-08-03 09:54, Yongji Xie wrote: > >>> On Tue, Aug 3, 2021 at 3:41 PM Jason Wang <jasowang@redhat.com> wrote: > >>>> > >>>> > >>>> 在 2021/7/29 下午3:34, Xie Yongji 写道: > >>>>> Export alloc_iova_fast() and free_iova_fast() so that > >>>>> some modules can use it to improve iova allocation efficiency. > >>>> > >>>> > >>>> It's better to explain why alloc_iova() is not sufficient here. > >>>> > >>> > >>> Fine. > >> > >> What I fail to understand from the later patches is what the IOVA domain > >> actually represents. If the "device" is a userspace process then > >> logically the "IOVA" would be the userspace address, so presumably > >> somewhere you're having to translate between this arbitrary address > >> space and actual usable addresses - if you're worried about efficiency > >> surely it would be even better to not do that? > >> > > > > Yes, userspace daemon needs to translate the "IOVA" in a DMA > > descriptor to the VA (from mmap(2)). But this actually doesn't affect > > performance since it's an identical mapping in most cases. > > I'm not familiar with the vhost_iotlb stuff, but it looks suspiciously > like you're walking yet another tree to make those translations. Even if > the buffer can be mapped all at once with a fixed offset such that each > DMA mapping call doesn't need a lookup for each individual "IOVA" - that > might be what's happening already, but it's a bit hard to follow just > reading the patches in my mail client - vhost_iotlb_add_range() doesn't > look like it's super-cheap to call, and you're serialising on a lock for > that. > Yes, that's true. Since the software IOTLB is not used in the VM case, we need a unified way (vhost_iotlb) to manage the IOVA mapping for both VM and Container cases. > My main point, though, is that if you've already got something else > keeping track of the actual addresses, then the way you're using an > iova_domain appears to be something you could do with a trivial bitmap > allocator. That's why I don't buy the efficiency argument. The main > design points of the IOVA allocator are to manage large address spaces > while trying to maximise spatial locality to minimise the underlying > pagetable usage, and allocating with a flexible limit to support > multiple devices with different addressing capabilities in the same > address space. If none of those aspects are relevant to the use-case - > which AFAICS appears to be true here - then as a general-purpose > resource allocator it's rubbish and has an unreasonably massive memory > overhead and there are many, many better choices. > OK, I get your point. Actually we used the genpool allocator in the early version. Maybe we can fall back to using it. > FWIW I've recently started thinking about moving all the caching stuff > out of iova_domain and into the iommu-dma layer since it's now a giant > waste of space for all the other current IOVA users. > > >> Presumably userspace doesn't have any concern about alignment and the > >> things we have to worry about for the DMA API in general, so it's pretty > >> much just allocating slots in a buffer, and there are far more effective > >> ways to do that than a full-blown address space manager. > > > > Considering iova allocation efficiency, I think the iova allocator is > > better here. In most cases, we don't even need to hold a spin lock > > during iova allocation. > > > >> If you're going > >> to reuse any infrastructure I'd have expected it to be SWIOTLB rather > >> than the IOVA allocator. Because, y'know, you're *literally implementing > >> a software I/O TLB* ;) > >> > > > > But actually what we can reuse in SWIOTLB is the IOVA allocator. > > Huh? Those are completely unrelated and orthogonal things - SWIOTLB does > not use an external allocator (see find_slots()). By SWIOTLB I mean > specifically the library itself, not dma-direct or any of the other > users built around it. The functionality for managing slots in a buffer > and bouncing data in and out can absolutely be reused - that's why users > like the Xen and iommu-dma code *are* reusing it instead of open-coding > their own versions. > I see. Actually the slots management in SWIOTLB is what I mean by IOVA allocator. > > And > > the IOVA management in SWIOTLB is not what we want. For example, > > SWIOTLB allocates and uses contiguous memory for bouncing, which is > > not necessary in VDUSE case. > > alloc_iova() allocates a contiguous (in IOVA address) region of space. > In vduse_domain_map_page() you use it to allocate a contiguous region of > space from your bounce buffer. Can you clarify how that is fundamentally > different from allocating a contiguous region of space from a bounce > buffer? Nobody's saying the underlying implementation details of where > the buffer itself comes from can't be tweaked. > I mean physically contiguous memory here. We can currently allocate the bounce pages one by one rather than allocating a bunch of physically contiguous memory at once which is not friendly to a userspace device. > > And VDUSE needs coherent mapping which is > > not supported by the SWIOTLB. Besides, the SWIOTLB works in singleton > > mode (designed for platform IOMMU) , but VDUSE is based on on-chip > > IOMMU (supports multiple instances). > That's not entirely true - the IOMMU bounce buffering scheme introduced > in intel-iommu and now moved into the iommu-dma layer was already a step > towards something conceptually similar. It does still rely on stealing > the underlying pages from the global SWIOTLB pool at the moment, but the > bouncing is effectively done in a per-IOMMU-domain context. > > The next step is currently queued in linux-next, wherein we can now have > individual per-device SWIOTLB pools. In fact at that point I think you > might actually be able to do your thing without implementing any special > DMA ops at all - you'd need to set up a pool for your "device" with > force_bounce set, then when you mmap() that to userspace, set up > dev->dma_range_map to describe an offset from the physical address of > the buffer to the userspace address, and I think dma-direct would be > tricked into doing the right thing. It's a bit wacky, but it could stand > to save a hell of a lot of bother. > Cool! I missed this work, sorry. But it looks like its current version can't meet our needs (e.g. avoid using physically contiguous memory). So I'd like to consider it as a follow-up optimization and use a general IOVA allocator in this initial version. The IOVA allocator would be still needed for coherent mapping (vduse_domain_alloc_coherent() and vduse_domain_free_coherent()) after we reuse the SWIOTLB. > Finally, enhancing SWIOTLB to cope with virtually-mapped buffers that > don't have to be physically contiguous is a future improvement which I > think could benefit various use-cases - indeed it's possibly already on > the table for IOMMU bounce pages - so would probably be welcome in general. > Yes, it's indeed needed by VDUSE. But I'm not sure if it would be needed by other drivers. Looks like we need swiotlb_tbl_map_single() to return a virtual address and introduce some way to let the caller do some translation between VA to PA. Thanks, Yongji
在 2021/8/5 下午8:34, Yongji Xie 写道: >> My main point, though, is that if you've already got something else >> keeping track of the actual addresses, then the way you're using an >> iova_domain appears to be something you could do with a trivial bitmap >> allocator. That's why I don't buy the efficiency argument. The main >> design points of the IOVA allocator are to manage large address spaces >> while trying to maximise spatial locality to minimise the underlying >> pagetable usage, and allocating with a flexible limit to support >> multiple devices with different addressing capabilities in the same >> address space. If none of those aspects are relevant to the use-case - >> which AFAICS appears to be true here - then as a general-purpose >> resource allocator it's rubbish and has an unreasonably massive memory >> overhead and there are many, many better choices. >> > OK, I get your point. Actually we used the genpool allocator in the > early version. Maybe we can fall back to using it. I think maybe you can share some perf numbers to see how much alloc_iova_fast() can help. Thanks >
On Thu, Aug 5, 2021 at 9:31 PM Jason Wang <jasowang@redhat.com> wrote: > > > 在 2021/8/5 下午8:34, Yongji Xie 写道: > >> My main point, though, is that if you've already got something else > >> keeping track of the actual addresses, then the way you're using an > >> iova_domain appears to be something you could do with a trivial bitmap > >> allocator. That's why I don't buy the efficiency argument. The main > >> design points of the IOVA allocator are to manage large address spaces > >> while trying to maximise spatial locality to minimise the underlying > >> pagetable usage, and allocating with a flexible limit to support > >> multiple devices with different addressing capabilities in the same > >> address space. If none of those aspects are relevant to the use-case - > >> which AFAICS appears to be true here - then as a general-purpose > >> resource allocator it's rubbish and has an unreasonably massive memory > >> overhead and there are many, many better choices. > >> > > OK, I get your point. Actually we used the genpool allocator in the > > early version. Maybe we can fall back to using it. > > > I think maybe you can share some perf numbers to see how much > alloc_iova_fast() can help. > I did some fio tests[1] with a ram-backend vduse block device[2]. Following are some performance data: numjobs=1 numjobs=2 numjobs=4 numjobs=8 iova_alloc_fast 145k iops 265k iops 514k iops 758k iops iova_alloc 137k iops 170k iops 128k iops 113k iops gen_pool_alloc 143k iops 270k iops 458k iops 521k iops The iova_alloc_fast() has the best performance since we always hit the per-cpu cache. Regardless of the per-cpu cache, the genpool allocator should be better than the iova allocator. [1] fio jobfile: [global] rw=randread direct=1 ioengine=libaio iodepth=16 time_based=1 runtime=60s group_reporting bs=4k filename=/dev/vda [job] numjobs=.. [2] $ qemu-storage-daemon \ --chardev socket,id=charmonitor,path=/tmp/qmp.sock,server,nowait \ --monitor chardev=charmonitor \ --blockdev driver=host_device,cache.direct=on,aio=native,filename=/dev/nullb0,node-name=disk0 \ --export type=vduse-blk,id=test,node-name=disk0,writable=on,name=vduse-null,num-queues=16,queue-size=128 The qemu-storage-daemon can be builded based on the repo: https://github.com/bytedance/qemu/tree/vduse-test. Thanks, Yongji
在 2021/8/9 下午1:56, Yongji Xie 写道: > On Thu, Aug 5, 2021 at 9:31 PM Jason Wang <jasowang@redhat.com> wrote: >> >> 在 2021/8/5 下午8:34, Yongji Xie 写道: >>>> My main point, though, is that if you've already got something else >>>> keeping track of the actual addresses, then the way you're using an >>>> iova_domain appears to be something you could do with a trivial bitmap >>>> allocator. That's why I don't buy the efficiency argument. The main >>>> design points of the IOVA allocator are to manage large address spaces >>>> while trying to maximise spatial locality to minimise the underlying >>>> pagetable usage, and allocating with a flexible limit to support >>>> multiple devices with different addressing capabilities in the same >>>> address space. If none of those aspects are relevant to the use-case - >>>> which AFAICS appears to be true here - then as a general-purpose >>>> resource allocator it's rubbish and has an unreasonably massive memory >>>> overhead and there are many, many better choices. >>>> >>> OK, I get your point. Actually we used the genpool allocator in the >>> early version. Maybe we can fall back to using it. >> >> I think maybe you can share some perf numbers to see how much >> alloc_iova_fast() can help. >> > I did some fio tests[1] with a ram-backend vduse block device[2]. > > Following are some performance data: > > numjobs=1 numjobs=2 numjobs=4 numjobs=8 > iova_alloc_fast 145k iops 265k iops 514k iops 758k iops > > iova_alloc 137k iops 170k iops 128k iops 113k iops > > gen_pool_alloc 143k iops 270k iops 458k iops 521k iops > > The iova_alloc_fast() has the best performance since we always hit the > per-cpu cache. Regardless of the per-cpu cache, the genpool allocator > should be better than the iova allocator. I think we see convincing numbers for using iova_alloc_fast() than the gen_poll_alloc() (45% improvement on job=8). Thanks > > [1] fio jobfile: > > [global] > rw=randread > direct=1 > ioengine=libaio > iodepth=16 > time_based=1 > runtime=60s > group_reporting > bs=4k > filename=/dev/vda > [job] > numjobs=.. > > [2] $ qemu-storage-daemon \ > --chardev socket,id=charmonitor,path=/tmp/qmp.sock,server,nowait \ > --monitor chardev=charmonitor \ > --blockdev > driver=host_device,cache.direct=on,aio=native,filename=/dev/nullb0,node-name=disk0 > \ > --export type=vduse-blk,id=test,node-name=disk0,writable=on,name=vduse-null,num-queues=16,queue-size=128 > > The qemu-storage-daemon can be builded based on the repo: > https://github.com/bytedance/qemu/tree/vduse-test. > > Thanks, > Yongji >
On Tue, Aug 10, 2021 at 11:02 AM Jason Wang <jasowang@redhat.com> wrote: > > > 在 2021/8/9 下午1:56, Yongji Xie 写道: > > On Thu, Aug 5, 2021 at 9:31 PM Jason Wang <jasowang@redhat.com> wrote: > >> > >> 在 2021/8/5 下午8:34, Yongji Xie 写道: > >>>> My main point, though, is that if you've already got something else > >>>> keeping track of the actual addresses, then the way you're using an > >>>> iova_domain appears to be something you could do with a trivial bitmap > >>>> allocator. That's why I don't buy the efficiency argument. The main > >>>> design points of the IOVA allocator are to manage large address spaces > >>>> while trying to maximise spatial locality to minimise the underlying > >>>> pagetable usage, and allocating with a flexible limit to support > >>>> multiple devices with different addressing capabilities in the same > >>>> address space. If none of those aspects are relevant to the use-case - > >>>> which AFAICS appears to be true here - then as a general-purpose > >>>> resource allocator it's rubbish and has an unreasonably massive memory > >>>> overhead and there are many, many better choices. > >>>> > >>> OK, I get your point. Actually we used the genpool allocator in the > >>> early version. Maybe we can fall back to using it. > >> > >> I think maybe you can share some perf numbers to see how much > >> alloc_iova_fast() can help. > >> > > I did some fio tests[1] with a ram-backend vduse block device[2]. > > > > Following are some performance data: > > > > numjobs=1 numjobs=2 numjobs=4 numjobs=8 > > iova_alloc_fast 145k iops 265k iops 514k iops 758k iops > > > > iova_alloc 137k iops 170k iops 128k iops 113k iops > > > > gen_pool_alloc 143k iops 270k iops 458k iops 521k iops > > > > The iova_alloc_fast() has the best performance since we always hit the > > per-cpu cache. Regardless of the per-cpu cache, the genpool allocator > > should be better than the iova allocator. > > > I think we see convincing numbers for using iova_alloc_fast() than the > gen_poll_alloc() (45% improvement on job=8). > Yes, so alloc_iova_fast() still seems to be the best choice based on performance considerations. Hi Robin, any comments? Thanks, Yongji
diff --git a/drivers/iommu/iova.c b/drivers/iommu/iova.c index b6cf5f16123b..3941ed6bb99b 100644 --- a/drivers/iommu/iova.c +++ b/drivers/iommu/iova.c @@ -521,6 +521,7 @@ alloc_iova_fast(struct iova_domain *iovad, unsigned long size, return new_iova->pfn_lo; } +EXPORT_SYMBOL_GPL(alloc_iova_fast); /** * free_iova_fast - free iova pfn range into rcache @@ -538,6 +539,7 @@ free_iova_fast(struct iova_domain *iovad, unsigned long pfn, unsigned long size) free_iova(iovad, pfn); } +EXPORT_SYMBOL_GPL(free_iova_fast); #define fq_ring_for_each(i, fq) \ for ((i) = (fq)->head; (i) != (fq)->tail; (i) = ((i) + 1) % IOVA_FQ_SIZE)
Export alloc_iova_fast() and free_iova_fast() so that some modules can use it to improve iova allocation efficiency. Signed-off-by: Xie Yongji <xieyongji@bytedance.com> --- drivers/iommu/iova.c | 2 ++ 1 file changed, 2 insertions(+)