From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934159AbcCPB47 (ORCPT ); Tue, 15 Mar 2016 21:56:59 -0400 Received: from szxga02-in.huawei.com ([119.145.14.65]:13652 "EHLO szxga02-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751293AbcCPB45 (ORCPT ); Tue, 15 Mar 2016 21:56:57 -0400 Subject: Re: [PATCH 1/1] arm64/dma-mapping: remove an unnecessary conversion To: Catalin Marinas References: <1458007931-14432-1-git-send-email-thunder.leizhen@huawei.com> <20160315153757.GF12311@e104818-lin.cambridge.arm.com> CC: Will Deacon , linux-kernel , Zefan Li , Xinwei Hu , Tianhong Ding , Hanjun Guo , linux-arm-kernel From: "Leizhen (ThunderTown)" Message-ID: <56E8BD51.6010008@huawei.com> Date: Wed, 16 Mar 2016 09:56:33 +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: <20160315153757.GF12311@e104818-lin.cambridge.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=0001.0A020201.56E8BD5D.00E9,ss=1,re=0.000,recu=0.000,reip=0.000,cl=1,cld=1,fgs=0, ip=0.0.0.0, so=2013-06-18 04:22:30, dmn=2013-03-21 17:37:32 X-Mirapoint-Loop-Id: 2c1ba99da7c3be5a0820bcbb72b92871 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2016/3/15 23:37, Catalin Marinas wrote: > On Tue, Mar 15, 2016 at 10:12:11AM +0800, Zhen Lei wrote: >> 1. In swiotlb_alloc_coherent, the branch of __get_free_pages. Directly >> return vaddr on success, and pass vaddr to free_pages on failure. >> 2. So, we can directly transparent pass vaddr from __dma_free to >> swiotlb_free_coherent, keep consistent with swiotlb_alloc_coherent. >> >> This patch have no functional change, > > I don't think so. > >> but can obtain a bit performance improvement. > > Have you actually measured it? I have not run any performance testing, but reduced a line of code. So I said "a bit". > >> diff --git a/arch/arm64/mm/dma-mapping.c b/arch/arm64/mm/dma-mapping.c >> index a6e757c..b2f2834 100644 >> --- a/arch/arm64/mm/dma-mapping.c >> +++ b/arch/arm64/mm/dma-mapping.c >> @@ -187,8 +187,6 @@ static void __dma_free(struct device *dev, size_t size, >> void *vaddr, dma_addr_t dma_handle, >> struct dma_attrs *attrs) >> { >> - void *swiotlb_addr = phys_to_virt(dma_to_phys(dev, dma_handle)); >> - >> size = PAGE_ALIGN(size); >> >> if (!is_device_dma_coherent(dev)) { >> @@ -196,7 +194,7 @@ static void __dma_free(struct device *dev, size_t size, >> return; >> vunmap(vaddr); >> } >> - __dma_free_coherent(dev, size, swiotlb_addr, dma_handle, attrs); >> + __dma_free_coherent(dev, size, vaddr, dma_handle, attrs); >> } > > What happens when !is_device_dma_coherent(dev)? (hint: read two lines > above __dma_free_coherent). > The whole function of __dma_free as below: (nobody use swiotlb_addr except __dma_free_coherent) static void __dma_free(struct device *dev, size_t size, void *vaddr, dma_addr_t dma_handle, struct dma_attrs *attrs) { void *swiotlb_addr = phys_to_virt(dma_to_phys(dev, dma_handle)); size = PAGE_ALIGN(size); if (!is_device_dma_coherent(dev)) { if (__free_from_pool(vaddr, size)) return; vunmap(vaddr); } __dma_free_coherent(dev, size, swiotlb_addr, dma_handle, attrs); }