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Wed, 26 Jun 2024 11:24:13 -0400 X-MC-Unique: cCHdZTlCNjm6naWohjJ3Cg-1 Received: from mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.4]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-02.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 8572919560B6; Wed, 26 Jun 2024 15:24:10 +0000 (UTC) Received: from [10.39.208.50] (unknown [10.39.208.50]) by mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 24CA6300021A; Wed, 26 Jun 2024 15:24:06 +0000 (UTC) Message-ID: Date: Wed, 26 Jun 2024 17:24:04 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 00/13] Optionally have rte_memcpy delegate to compiler memcpy To: Stephen Hemminger Cc: =?UTF-8?Q?Mattias_R=C3=B6nnblom?= , =?UTF-8?Q?Mattias_R=C3=B6nnblom?= , dev@dpdk.org, =?UTF-8?Q?Morten_Br=C3=B8rup?= , Abdullah Sevincer , Pavan Nikhilesh , David Hunt , Vladimir Medvedkin , Bruce Richardson References: <20240620115027.420304-2-mattias.ronnblom@ericsson.com> <20240620175731.420639-1-mattias.ronnblom@ericsson.com> <3eebd7f7-9ba2-424c-80d1-6efa8945641d@redhat.com> <20240626075841.5e63e7c0@hermes.local> From: Maxime Coquelin Autocrypt: addr=maxime.coquelin@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-BeenThere: dev@dpdk.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: DPDK patches and discussions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dev-bounces@dpdk.org On 6/26/24 16:58, Stephen Hemminger wrote: > On Wed, 26 Jun 2024 10:37:31 +0200 > Maxime Coquelin wrote: > >> On 6/25/24 21:27, Mattias Rönnblom wrote: >>> On Tue, Jun 25, 2024 at 05:29:35PM +0200, Maxime Coquelin wrote: >>>> Hi Mattias, >>>> >>>> On 6/20/24 19:57, Mattias Rönnblom wrote: >>>>> This patch set make DPDK library, driver, and application code use the >>>>> compiler/libc memcpy() by default when functions in are >>>>> invoked. >>>>> >>>>> The various custom DPDK rte_memcpy() implementations may be retained >>>>> by means of a build-time option. >>>>> >>>>> This patch set only make a difference on x86, PPC and ARM. Loongarch >>>>> and RISCV already used compiler/libc memcpy(). >>>> >>>> It indeed makes a difference on x86! >>>> >>>> Just tested latest main with and without your series on >>>> Intel(R) Xeon(R) Gold 6438N. >>>> >>>> The test is a simple IO loop between a Vhost PMD and a Virtio-user PMD: >>>> # dpdk-testpmd -l 4-6 --file-prefix=virtio1 --no-pci --vdev 'net_virtio_user0,mac=00:01:02:03:04:05,path=./vhost-net,server=1,mrg_rxbuf=1,in_order=1' >>>> --single-file-segments -- -i >>>> testpmd> start >>>> >>>> # dpdk-testpmd -l 8-10 --file-prefix=vhost1 --no-pci --vdev >>>> 'net_vhost0,iface=vhost-net,client=1' --single-file-segments -- -i >>>> testpmd> start tx_first 32 >>>> >>>> Latest main: 14.5Mpps >>>> Latest main + this series: 10Mpps >>>> >>> >>> I ran the above benchmark on my Raptor Lake desktop (locked to 3,2 >>> GHz). GCC 12.3.0. >>> >>> Core use_cc_memcpy Mpps >>> E false 9.5 >>> E true 9.7 >>> P false 16.4 >>> P true 13.5 >>> >>> On the P-cores, there's a significant performance regression, although >>> not as bad as the one you see on your Sapphire Rapids Xeon. On the >>> E-cores, there's actually a slight performance gain. >>> >>> The virtio PMD does not directly invoke rte_memcpy() or anything else >>> from , but rather use memcpy(), so I'm not sure I >>> understand what's going on here. Does the virtio driver delegate some >>> performance-critical task to some module that in turns uses >>> rte_memcpy()? >> >> This is because Vhost is the bottleneck here, not Virtio driver. >> Indeed, the virtqueues memory belongs to the Virtio driver and the >> descriptors buffers are Virtio's mbufs, so not much memcpy's are done >> there. >> >> Vhost however, is a heavy memcpy user, as all the descriptors buffers >> are copied to/from its mbufs. > > Would be good to now the size (if small it is inlining that matters, or > maybe alignment matters), and have test results for multiple compiler versions. > Ideally, feed results back and update Gcc and Clang. I was testing with GCC 11 on RHEL-9: gcc (GCC) 11.4.1 20231218 (Red Hat 11.4.1-3) I was using the default one, 64B packets. I don't have time to perform these tests, but if you are willing to do it I'll be happy to review the results. > DPDK doesn't need to be in the optimize C library space. Certainly, but we already have an optimized version currently, so not much to do now on our side. When C libraries implementations will be on par, we should definitely use them by default. Maxime