From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Leizhen (ThunderTown)" Subject: Re: [PATCH 2/7] iommu/iova: cut down judgement times Date: Fri, 31 Mar 2017 11:55:38 +0800 Message-ID: <58DDD33A.2040807@huawei.com> References: <1490164067-12552-1-git-send-email-thunder.leizhen@huawei.com> <1490164067-12552-3-git-send-email-thunder.leizhen@huawei.com> <2884b8d1-72d4-dc41-75c1-92cfa19d77ae@arm.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <2884b8d1-72d4-dc41-75c1-92cfa19d77ae-5wv7dgnIgG8@public.gmane.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: iommu-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org Errors-To: iommu-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org To: Robin Murphy , Joerg Roedel , iommu , David Woodhouse , Sudeep Dutt , Ashutosh Dixit , linux-kernel Cc: Xinwei Hu , Zefan Li , Hanjun Guo , Tianhong Ding List-Id: iommu@lists.linux-foundation.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 > >> Signed-off-by: Zhen Lei >> --- >> 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 From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932683AbdCaD51 (ORCPT ); Thu, 30 Mar 2017 23:57:27 -0400 Received: from szxga01-in.huawei.com ([45.249.212.187]:5277 "EHLO dggrg01-dlp.huawei.com" rhost-flags-OK-FAIL-OK-FAIL) by vger.kernel.org with ESMTP id S932265AbdCaD50 (ORCPT ); Thu, 30 Mar 2017 23:57:26 -0400 Subject: Re: [PATCH 2/7] iommu/iova: cut down judgement times To: Robin Murphy , Joerg Roedel , iommu , David Woodhouse , Sudeep Dutt , Ashutosh Dixit , linux-kernel References: <1490164067-12552-1-git-send-email-thunder.leizhen@huawei.com> <1490164067-12552-3-git-send-email-thunder.leizhen@huawei.com> <2884b8d1-72d4-dc41-75c1-92cfa19d77ae@arm.com> CC: Zefan Li , Xinwei Hu , "Tianhong Ding" , Hanjun Guo From: "Leizhen (ThunderTown)" Message-ID: <58DDD33A.2040807@huawei.com> Date: Fri, 31 Mar 2017 11:55:38 +0800 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:38.0) Gecko/20100101 Thunderbird/38.5.1 MIME-Version: 1.0 In-Reply-To: <2884b8d1-72d4-dc41-75c1-92cfa19d77ae@arm.com> Content-Type: text/plain; charset="windows-1252" Content-Transfer-Encoding: 7bit X-Originating-IP: [10.177.23.164] X-CFilter-Loop: Reflected X-Mirapoint-Virus-RAPID-Raw: score=unknown(0), refid=str=0001.0A090202.58DDD346.006F,ss=1,re=0.000,recu=0.000,reip=0.000,cl=1,cld=1,fgs=0, ip=0.0.0.0, so=2014-11-16 11:51:01, dmn=2013-03-21 17:37:32 X-Mirapoint-Loop-Id: e6c362fca068ce80874da7e980978a46 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.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 > >> Signed-off-by: Zhen Lei >> --- >> 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