From: "Leizhen (ThunderTown)" <thunder.leizhen@huawei.com> To: Robin Murphy <robin.murphy@arm.com>, Joerg Roedel <joro@8bytes.org>, iommu <iommu@lists.linux-foundation.org>, David Woodhouse <dwmw2@infradead.org>, Sudeep Dutt <sudeep.dutt@intel.com>, Ashutosh Dixit <ashutosh.dixit@intel.com>, linux-kernel <linux-kernel@vger.kernel.org> Cc: Zefan Li <lizefan@huawei.com>, Xinwei Hu <huxinwei@huawei.com>, "Tianhong Ding" <dingtianhong@huawei.com>, Hanjun Guo <guohanjun@huawei.com> Subject: Re: [PATCH 2/7] iommu/iova: cut down judgement times Date: Fri, 31 Mar 2017 11:55:38 +0800 [thread overview] Message-ID: <58DDD33A.2040807@huawei.com> (raw) In-Reply-To: <2884b8d1-72d4-dc41-75c1-92cfa19d77ae@arm.com> 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
WARNING: multiple messages have this Message-ID (diff)
From: "Leizhen (ThunderTown)" <thunder.leizhen-hv44wF8Li93QT0dZR+AlfA@public.gmane.org> To: Robin Murphy <robin.murphy-5wv7dgnIgG8@public.gmane.org>, Joerg Roedel <joro-zLv9SwRftAIdnm+yROfE0A@public.gmane.org>, iommu <iommu-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org>, David Woodhouse <dwmw2-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org>, Sudeep Dutt <sudeep.dutt-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>, Ashutosh Dixit <ashutosh.dixit-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>, linux-kernel <linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org> Cc: Xinwei Hu <huxinwei-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>, Zefan Li <lizefan-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>, Hanjun Guo <guohanjun-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>, Tianhong Ding <dingtianhong-hv44wF8Li93QT0dZR+AlfA@public.gmane.org> Subject: Re: [PATCH 2/7] iommu/iova: cut down judgement times Date: Fri, 31 Mar 2017 11:55:38 +0800 [thread overview] Message-ID: <58DDD33A.2040807@huawei.com> (raw) In-Reply-To: <2884b8d1-72d4-dc41-75c1-92cfa19d77ae-5wv7dgnIgG8@public.gmane.org> 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-5wv7dgnIgG8@public.gmane.org> > >> Signed-off-by: Zhen Lei <thunder.leizhen-hv44wF8Li93QT0dZR+AlfA@public.gmane.org> >> --- >> 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
next prev parent reply other threads:[~2017-03-31 3:57 UTC|newest] Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top 2017-03-22 6:27 [PATCH 0/7] iommu/iova: improve the allocation performance of dma64 Zhen Lei 2017-03-22 6:27 ` Zhen Lei 2017-03-22 6:27 ` [PATCH 1/7] iommu/iova: fix incorrect variable types Zhen Lei 2017-03-22 6:27 ` Zhen Lei 2017-03-23 11:42 ` Robin Murphy 2017-03-24 2:27 ` Leizhen (ThunderTown) 2017-03-24 2:27 ` Leizhen (ThunderTown) 2017-03-31 3:30 ` Leizhen (ThunderTown) 2017-03-31 3:30 ` Leizhen (ThunderTown) 2017-03-22 6:27 ` [PATCH 2/7] iommu/iova: cut down judgement times Zhen Lei 2017-03-22 6:27 ` Zhen Lei 2017-03-23 12:11 ` Robin Murphy 2017-03-23 12:11 ` Robin Murphy 2017-03-31 3:55 ` Leizhen (ThunderTown) [this message] 2017-03-31 3:55 ` Leizhen (ThunderTown) 2017-03-22 6:27 ` [PATCH 3/7] iommu/iova: insert start_pfn boundary of dma32 Zhen Lei 2017-03-22 6:27 ` Zhen Lei 2017-03-23 13:01 ` Robin Murphy 2017-03-23 13:01 ` Robin Murphy 2017-03-24 3:43 ` Leizhen (ThunderTown) 2017-03-24 3:43 ` Leizhen (ThunderTown) 2017-03-31 3:32 ` Leizhen (ThunderTown) 2017-03-31 3:32 ` Leizhen (ThunderTown) 2017-03-22 6:27 ` [PATCH 4/7] iommu/iova: adjust __cached_rbnode_insert_update Zhen Lei 2017-03-22 6:27 ` Zhen Lei 2017-03-22 6:27 ` [PATCH 5/7] iommu/iova: to optimize the allocation performance of dma64 Zhen Lei 2017-03-22 6:27 ` Zhen Lei 2017-03-22 6:27 ` [PATCH 6/7] iommu/iova: move the caculation of pad mask out of loop Zhen Lei 2017-03-22 6:27 ` Zhen Lei 2017-03-22 6:27 ` [PATCH 7/7] iommu/iova: fix iovad->dma_32bit_pfn as the last pfn of dma32 Zhen Lei 2017-03-22 6:27 ` Zhen Lei
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