| Message ID | 20210827005228.15671-1-kangning18z@ict.ac.cn (mailing list archive) |
|---|---|
| State | Awaiting Upstream |
| Headers | show |
| Series | [v3] Fix one error in mthca_alloc | expand |
On Fri, Aug 27, 2021 at 08:52:28AM +0800, kangning wrote: > drivers/infiniband/hw/mthca/mthca_allocator.c: alloc->last left unchanged in mthca_alloc, which > has impact on performance of function find_next_zero_bit in mthca_alloc. I don't know what the sentence above means, but the change is unlikely to be correct. When alloc->last starts to be equal to alloc->max, the find_next_zero_bit() will always return alloc->max. which will ensure that the following code is executed. 48 if (obj >= alloc->max) { 49 alloc->top = (alloc->top + alloc->max) & alloc->mask; 50 obj = find_first_zero_bit(alloc->table, alloc->max); 51 } However the mthca_alloc() function has other error, it returns -1 while based on its declaration it needs to be unsigned, Thanks > > Signed-off-by: kangning <kangning18z@ict.ac.cn> > --- > > I squashed two commits into one in this version. > > drivers/infiniband/hw/mthca/mthca_allocator.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/drivers/infiniband/hw/mthca/mthca_allocator.c b/drivers/infiniband/hw/mthca/mthca_allocator.c > index aef1d274a14e..1141695093e7 100644 > --- a/drivers/infiniband/hw/mthca/mthca_allocator.c > +++ b/drivers/infiniband/hw/mthca/mthca_allocator.c > @@ -51,6 +51,9 @@ u32 mthca_alloc(struct mthca_alloc *alloc) > } > > if (obj < alloc->max) { > + alloc->last = obj + 1; > + if (alloc->last == alloc->max) > + alloc->last = 0; > set_bit(obj, alloc->table); > obj |= alloc->top; > } else > -- > 2.17.1 >
>
> On Fri, Aug 27, 2021 at 08:52:28AM +0800, kangning wrote:
> > drivers/infiniband/hw/mthca/mthca_allocator.c: alloc->last left unchanged in mthca_alloc, which
> > has impact on performance of function find_next_zero_bit in mthca_alloc.
>
> I don't know what the sentence above means, but the change is unlikely
> to be correct.
>
> When alloc->last starts to be equal to alloc->max, the
> find_next_zero_bit() will always return alloc->max. which will ensure
> that the following code is executed.
>
> 48 if (obj >= alloc->max) {
> 49 alloc->top = (alloc->top + alloc->max) & alloc->mask;
> 50 obj = find_first_zero_bit(alloc->table, alloc->max);
> 51 }
>
Thanks for your review.
Yes, your analysis is right. However, this is a bitmap allocator for resource id allocation (like QP, and CQ).
We first look at the situation where no resource id is released.
When the value of alloc->last starts to reaches alloc->max, the bitmap will
be full. In this case, it's normal to return an invalid value.
Now, let's add resource releasing into consideration.
The following code is part of mthca_free：
70 spin_lock_irqsave(&alloc->lock, flags);
71
72 clear_bit(obj, alloc->table);
73 alloc->last = min(alloc->last, obj);
74 alloc->top = (alloc->top + alloc->max) & alloc->mask;
mthca_free() is used to release the allocated resource id. It will update alloc->last when obj is freed.
So, if the bitmap has space for allocation, my modification can continuously work.
>
> However the mthca_alloc() function has other error, it returns -1 while
> based on its declaration it needs to be unsigned,
I think you are right about this. But obj is the return value of u32 type, which is the requirement of resource id
(though it may not fully use 32 bits). I have no idea of how to fix it.
Thanks.
>
> Thanks
>
> >
> > Signed-off-by: kangning <kangning18z@ict.ac.cn>
> > ---
> >
> > I squashed two commits into one in this version.
> >
> > drivers/infiniband/hw/mthca/mthca_allocator.c | 3 +++
> > 1 file changed, 3 insertions(+)
> >
> > diff --git a/drivers/infiniband/hw/mthca/mthca_allocator.c b/drivers/infiniband/hw/mthca/mthca_allocator.c
> > index aef1d274a14e..1141695093e7 100644
> > --- a/drivers/infiniband/hw/mthca/mthca_allocator.c
> > +++ b/drivers/infiniband/hw/mthca/mthca_allocator.c
> > @@ -51,6 +51,9 @@ u32 mthca_alloc(struct mthca_alloc *alloc)
> > }
> >
> > if (obj < alloc->max) {
> > + alloc->last = obj + 1;
> > + if (alloc->last == alloc->max)
> > + alloc->last = 0;
> > set_bit(obj, alloc->table);
> > obj |= alloc->top;
> > } else
> > --
> > 2.17.1
> >
</kangning18z@ict.ac.cn>
>
> On Fri, Aug 27, 2021 at 08:52:28AM +0800, kangning wrote:
> > drivers/infiniband/hw/mthca/mthca_allocator.c: alloc->last left unchanged in mthca_alloc, which
> > has impact on performance of function find_next_zero_bit in mthca_alloc.
>
> I don't know what the sentence above means, but the change is unlikely
> to be correct.
>
> When alloc->last starts to be equal to alloc->max, the
> find_next_zero_bit() will always return alloc->max. which will ensure
> that the following code is executed.
>
> 48 if (obj >= alloc->max) {
> 49 alloc->top = (alloc->top + alloc->max) & alloc->mask;
> 50 obj = find_first_zero_bit(alloc->table, alloc->max);
> 51 }
>
Thanks for your review.
Your analysis is right. However, this is a bitmap allocator for resource id allocation (like QP, and CQ).
We first look at the situation where no resource id is released.
When the value of alloc->last starts to reaches alloc->max, the bitmap will
be full. In this case, it's normal to return an invalid value.
Now, let's add resource releasing into consideration.
The following code is part of mthca_free()：
70 spin_lock_irqsave(&alloc->lock, flags);
71
72 clear_bit(obj, alloc->table);
73 alloc->last = min(alloc->last, obj);
74 alloc->top = (alloc->top + alloc->max) & alloc->mask;
mthca_free() is used to release the allocated resource id. It will update alloc->last when obj is freed.
So, if the bitmap has space for allocation, my modification can continuously work.
>
> However the mthca_alloc() function has other error, it returns -1 while
> based on its declaration it needs to be unsigned,
I think you are right about this. But obj is the return value of u32 type, which is the requirement of resource id
(though it may not fully use 32 bits). I have no idea of how to fix it.
Thanks.
>
> Thanks
>
> >
> > Signed-off-by: kangning <kangning18z@ict.ac.cn>
> > ---
> >
> > I squashed two commits into one in this version.
> >
> > drivers/infiniband/hw/mthca/mthca_allocator.c | 3 +++
> > 1 file changed, 3 insertions(+)
> >
> > diff --git a/drivers/infiniband/hw/mthca/mthca_allocator.c b/drivers/infiniband/hw/mthca/mthca_allocator.c
> > index aef1d274a14e..1141695093e7 100644
> > --- a/drivers/infiniband/hw/mthca/mthca_allocator.c
> > +++ b/drivers/infiniband/hw/mthca/mthca_allocator.c
> > @@ -51,6 +51,9 @@ u32 mthca_alloc(struct mthca_alloc *alloc)
> > }
> >
> > if (obj < alloc->max) {
> > + alloc->last = obj + 1;
> > + if (alloc->last == alloc->max)
> > + alloc->last = 0;
> > set_bit(obj, alloc->table);
> > obj |= alloc->top;
> > } else
> > --
> > 2.17.1
> >
</kangning18z@ict.ac.cn>
On Tue, Aug 31, 2021 at 06:40:38PM +0800, 康宁 wrote: > > > > On Fri, Aug 27, 2021 at 08:52:28AM +0800, kangning wrote: > > > drivers/infiniband/hw/mthca/mthca_allocator.c: alloc->last left unchanged in mthca_alloc, which > > > has impact on performance of function find_next_zero_bit in mthca_alloc. > > > > I don't know what the sentence above means, but the change is unlikely > > to be correct. > > > > When alloc->last starts to be equal to alloc->max, the > > find_next_zero_bit() will always return alloc->max. which will ensure > > that the following code is executed. > > > > 48 if (obj >= alloc->max) { > > 49 alloc->top = (alloc->top + alloc->max) & alloc->mask; > > 50 obj = find_first_zero_bit(alloc->table, alloc->max); > > 51 } > > > > Thanks for your review. > Yes, your analysis is right. However, this is a bitmap allocator for resource id allocation (like QP, and CQ). > We first look at the situation where no resource id is released. > When the value of alloc->last starts to reaches alloc->max, the bitmap will > be full. In this case, it's normal to return an invalid value. > > Now, let's add resource releasing into consideration. > The following code is part of mthca_free： > > 70 spin_lock_irqsave(&alloc->lock, flags); > 71 > 72 clear_bit(obj, alloc->table); > 73 alloc->last = min(alloc->last, obj); > 74 alloc->top = (alloc->top + alloc->max) & alloc->mask; > > mthca_free() is used to release the allocated resource id. It will update alloc->last when obj is freed. > So, if the bitmap has space for allocation, my modification can continuously work. After alloc->last starts to be equal to alloc->max, the bitmap is searches with find_first_zero_bit() call. That will ensure that we look for any bit between 0 and alloc->max. So no, your change can't be right. Thanks > > > > > However the mthca_alloc() function has other error, it returns -1 while > > based on its declaration it needs to be unsigned, > > I think you are right about this. But obj is the return value of u32 type, which is the requirement of resource id > (though it may not fully use 32 bits). I have no idea of how to fix it. > > Thanks. > > > > > Thanks > > > > > > > > Signed-off-by: kangning <kangning18z@ict.ac.cn> > > > --- > > > > > > I squashed two commits into one in this version. > > > > > > drivers/infiniband/hw/mthca/mthca_allocator.c | 3 +++ > > > 1 file changed, 3 insertions(+) > > > > > > diff --git a/drivers/infiniband/hw/mthca/mthca_allocator.c b/drivers/infiniband/hw/mthca/mthca_allocator.c > > > index aef1d274a14e..1141695093e7 100644 > > > --- a/drivers/infiniband/hw/mthca/mthca_allocator.c > > > +++ b/drivers/infiniband/hw/mthca/mthca_allocator.c > > > @@ -51,6 +51,9 @@ u32 mthca_alloc(struct mthca_alloc *alloc) > > > } > > > > > > if (obj < alloc->max) { > > > + alloc->last = obj + 1; > > > + if (alloc->last == alloc->max) > > > + alloc->last = 0; > > > set_bit(obj, alloc->table); > > > obj |= alloc->top; > > > } else > > > -- > > > 2.17.1 > > > > </kangning18z@ict.ac.cn>
> On Tue, Aug 31, 2021 at 06:40:38PM +0800, 康宁 wrote: > > > > > > On Fri, Aug 27, 2021 at 08:52:28AM +0800, kangning wrote: > > > > drivers/infiniband/hw/mthca/mthca_allocator.c: alloc->last left unchanged in mthca_alloc, which > > > > has impact on performance of function find_next_zero_bit in mthca_alloc. > > > > > > I don't know what the sentence above means, but the change is unlikely > > > to be correct. > > > > > > When alloc->last starts to be equal to alloc->max, the > > > find_next_zero_bit() will always return alloc->max. which will ensure > > > that the following code is executed. > > > > > > 48 if (obj >= alloc->max) { > > > 49 alloc->top = (alloc->top + alloc->max) & alloc->mask; > > > 50 obj = find_first_zero_bit(alloc->table, alloc->max); > > > 51 } > > > > > > > Thanks for your review. > > Yes, your analysis is right. However, this is a bitmap allocator for resource id allocation (like QP, and CQ). > > We first look at the situation where no resource id is released. > > When the value of alloc->last starts to reaches alloc->max, the bitmap will > > be full. In this case, it's normal to return an invalid value. > > > > Now, let's add resource releasing into consideration. > > The following code is part of mthca_free： > > > > 70 spin_lock_irqsave(&alloc->lock, flags); > > 71 > > 72 clear_bit(obj, alloc->table); > > 73 alloc->last = min(alloc->last, obj); > > 74 alloc->top = (alloc->top + alloc->max) & alloc->mask; > > > > mthca_free() is used to release the allocated resource id. It will update alloc->last when obj is freed. > > So, if the bitmap has space for allocation, my modification can continuously work. > > After alloc->last starts to be equal to alloc->max, the bitmap is > searches with find_first_zero_bit() call. That will ensure that we look > for any bit between 0 and alloc->max. > > So no, your change can't be right. If you never call function mthca_free(), you will never find a valid bit in [0, alloc->max] with find_first_zero_bit() call. Cause every bits between 0 and alloc->max are alloacted. But if you called mthca_free() before, the freed obj is assigned to alloc->last, and we still can allocate the bitmap. My modification is correct. > > Thanks > > > > > > > > > However the mthca_alloc() function has other error, it returns -1 while > > > based on its declaration it needs to be unsigned, > > > > I think you are right about this. But obj is the return value of u32 type, which is the requirement of resource id > > (though it may not fully use 32 bits). I have no idea of how to fix it. > > > > Thanks. > > > > > > > > Thanks > > > > > > > > > > > Signed-off-by: kangning <kangning18z@ict.ac.cn> > > > > --- > > > > > > > > I squashed two commits into one in this version. > > > > > > > > drivers/infiniband/hw/mthca/mthca_allocator.c | 3 +++ > > > > 1 file changed, 3 insertions(+) > > > > > > > > diff --git a/drivers/infiniband/hw/mthca/mthca_allocator.c b/drivers/infiniband/hw/mthca/mthca_allocator.c > > > > index aef1d274a14e..1141695093e7 100644 > > > > --- a/drivers/infiniband/hw/mthca/mthca_allocator.c > > > > +++ b/drivers/infiniband/hw/mthca/mthca_allocator.c > > > > @@ -51,6 +51,9 @@ u32 mthca_alloc(struct mthca_alloc *alloc) > > > > } > > > > > > > > if (obj < alloc->max) { > > > > + alloc->last = obj + 1; > > > > + if (alloc->last == alloc->max) > > > > + alloc->last = 0; > > > > set_bit(obj, alloc->table); > > > > obj |= alloc->top; > > > > } else > > > > -- > > > > 2.17.1 > > > > > > </kangning18z@ict.ac.cn>
On Wed, Sep 01, 2021 at 10:27:46AM +0800, kangning18z@ict.ac.cn wrote: > <...> > Thank you for your review. Do you have mthca card in hand to test your changes? This driver didn't get any changes for a long time and we don't even know if it works or not. I would prefer to minimize changes to that driver. Thanks
diff --git a/drivers/infiniband/hw/mthca/mthca_allocator.c b/drivers/infiniband/hw/mthca/mthca_allocator.c index aef1d274a14e..1141695093e7 100644 --- a/drivers/infiniband/hw/mthca/mthca_allocator.c +++ b/drivers/infiniband/hw/mthca/mthca_allocator.c @@ -51,6 +51,9 @@ u32 mthca_alloc(struct mthca_alloc *alloc) } if (obj < alloc->max) { + alloc->last = obj + 1; + if (alloc->last == alloc->max) + alloc->last = 0; set_bit(obj, alloc->table); obj |= alloc->top; } else
drivers/infiniband/hw/mthca/mthca_allocator.c: alloc->last left unchanged in mthca_alloc, which has impact on performance of function find_next_zero_bit in mthca_alloc. Signed-off-by: kangning <kangning18z@ict.ac.cn> --- I squashed two commits into one in this version. drivers/infiniband/hw/mthca/mthca_allocator.c | 3 +++ 1 file changed, 3 insertions(+)