| Message ID | 1490164067-12552-3-git-send-email-thunder.leizhen@huawei.com |
|---|---|
| State | Superseded |
| Headers | show |
| Series | iommu/iova: improve the allocation performance of dma64 | expand |
On 22/03/17 06:27, Zhen Lei wrote: > Below judgement can only be satisfied at the last time, which produced 2N > judgements(suppose N times failed, 0 or 1 time successed) in vain. > > if ((pfn >= iova->pfn_lo) && (pfn <= iova->pfn_hi)) { > return iova; > } For me, GCC (6.2.1 AArch64) seems to do a pretty good job of this function already, so this change only saves two instructions in total (pfn is compared against pfn_lo only once instead of twice), which I wouldn't expect to see a noticeable performance effect from. Given the improvement in readability, though, I don't even care about any codegen differences :) Reviewed-by: Robin Murphy <robin.murphy@arm.com> > Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com> > --- > drivers/iommu/iova.c | 9 +++------ > 1 file changed, 3 insertions(+), 6 deletions(-) > > diff --git a/drivers/iommu/iova.c b/drivers/iommu/iova.c > index 8ba8b496..1c49969 100644 > --- a/drivers/iommu/iova.c > +++ b/drivers/iommu/iova.c > @@ -312,15 +312,12 @@ private_find_iova(struct iova_domain *iovad, unsigned long pfn) > while (node) { > struct iova *iova = rb_entry(node, struct iova, node); > > - /* If pfn falls within iova's range, return iova */ > - if ((pfn >= iova->pfn_lo) && (pfn <= iova->pfn_hi)) { > - return iova; > - } > - > if (pfn < iova->pfn_lo) > node = node->rb_left; > - else if (pfn > iova->pfn_lo) > + else if (pfn > iova->pfn_hi) > node = node->rb_right; > + else > + return iova; /* pfn falls within iova's range */ > } > > return NULL; >
On 2017/3/23 20:11, Robin Murphy wrote: > On 22/03/17 06:27, Zhen Lei wrote: >> Below judgement can only be satisfied at the last time, which produced 2N >> judgements(suppose N times failed, 0 or 1 time successed) in vain. >> >> if ((pfn >= iova->pfn_lo) && (pfn <= iova->pfn_hi)) { >> return iova; >> } > > For me, GCC (6.2.1 AArch64) seems to do a pretty good job of this > function already, so this change only saves two instructions in total > (pfn is compared against pfn_lo only once instead of twice), which I > wouldn't expect to see a noticeable performance effect from. OK, thanks for your careful analysis. Although only two instructions saved in each loop iteration, but it's also an improvment and no harm. > > Given the improvement in readability, though, I don't even care about > any codegen differences :) > > Reviewed-by: Robin Murphy <robin.murphy@arm.com> > >> Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com> >> --- >> drivers/iommu/iova.c | 9 +++------ >> 1 file changed, 3 insertions(+), 6 deletions(-) >> >> diff --git a/drivers/iommu/iova.c b/drivers/iommu/iova.c >> index 8ba8b496..1c49969 100644 >> --- a/drivers/iommu/iova.c >> +++ b/drivers/iommu/iova.c >> @@ -312,15 +312,12 @@ private_find_iova(struct iova_domain *iovad, unsigned long pfn) >> while (node) { >> struct iova *iova = rb_entry(node, struct iova, node); >> >> - /* If pfn falls within iova's range, return iova */ >> - if ((pfn >= iova->pfn_lo) && (pfn <= iova->pfn_hi)) { >> - return iova; >> - } >> - >> if (pfn < iova->pfn_lo) >> node = node->rb_left; >> - else if (pfn > iova->pfn_lo) >> + else if (pfn > iova->pfn_hi) >> node = node->rb_right; >> + else >> + return iova; /* pfn falls within iova's range */ >> } >> >> return NULL; >> > > > . > -- Thanks! BestRegards
diff --git a/drivers/iommu/iova.c b/drivers/iommu/iova.c index 8ba8b496..1c49969 100644 --- a/drivers/iommu/iova.c +++ b/drivers/iommu/iova.c @@ -312,15 +312,12 @@ private_find_iova(struct iova_domain *iovad, unsigned long pfn) while (node) { struct iova *iova = rb_entry(node, struct iova, node); - /* If pfn falls within iova's range, return iova */ - if ((pfn >= iova->pfn_lo) && (pfn <= iova->pfn_hi)) { - return iova; - } - if (pfn < iova->pfn_lo) node = node->rb_left; - else if (pfn > iova->pfn_lo) + else if (pfn > iova->pfn_hi) node = node->rb_right; + else + return iova; /* pfn falls within iova's range */ } return NULL;
Below judgement can only be satisfied at the last time, which produced 2N judgements(suppose N times failed, 0 or 1 time successed) in vain. if ((pfn >= iova->pfn_lo) && (pfn <= iova->pfn_hi)) { return iova; } Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com> --- drivers/iommu/iova.c | 9 +++------ 1 file changed, 3 insertions(+), 6 deletions(-) -- 2.5.0