From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mails.dpdk.org (mails.dpdk.org [217.70.189.124]) by inbox.dpdk.org (Postfix) with ESMTP id 7669A45502; Thu, 27 Jun 2024 13:07:49 +0200 (CEST) Received: from mails.dpdk.org (localhost [127.0.0.1]) by mails.dpdk.org (Postfix) with ESMTP id 1A71E40BA3; Thu, 27 Jun 2024 13:07:49 +0200 (CEST) Received: from mail.lysator.liu.se (mail.lysator.liu.se [130.236.254.3]) by mails.dpdk.org (Postfix) with ESMTP id 0E24F40B99 for ; Thu, 27 Jun 2024 13:06:26 +0200 (CEST) Received: from mail.lysator.liu.se (localhost [127.0.0.1]) by mail.lysator.liu.se (Postfix) with ESMTP id F1D0697EA; Thu, 27 Jun 2024 13:06:24 +0200 (CEST) Received: from isengard (h-62-63-215-114.A163.priv.bahnhof.se [62.63.215.114]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange ECDHE (prime256v1) server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mail.lysator.liu.se (Postfix) with ESMTPSA id AD43498A7; Thu, 27 Jun 2024 13:06:23 +0200 (CEST) Date: Thu, 27 Jun 2024 13:06:22 +0200 From: Mattias =?iso-8859-1?Q?R=F6nnblom?= To: Morten =?iso-8859-1?Q?Br=F8rup?= Cc: Maxime Coquelin , Stephen Hemminger , Mattias =?iso-8859-1?Q?R=F6nnblom?= , dev@dpdk.org, Abdullah Sevincer , Pavan Nikhilesh , David Hunt , Vladimir Medvedkin , Bruce Richardson Subject: Re: [PATCH v4 00/13] Optionally have rte_memcpy delegate to compiler memcpy Message-ID: 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> <98CBD80474FA8B44BF855DF32C47DC35E9F55F@smartserver.smartshare.dk> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <98CBD80474FA8B44BF855DF32C47DC35E9F55F@smartserver.smartshare.dk> X-Virus-Scanned: ClamAV using ClamSMTP 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 Wed, Jun 26, 2024 at 10:16:06PM +0200, Morten Brørup wrote: > > From: Mattias Rönnblom [mailto:hofors@lysator.liu.se] > > Sent: Wednesday, 26 June 2024 20.48 > > > > On Wed, Jun 26, 2024 at 05:24:04PM +0200, Maxime Coquelin wrote: > > > > > > > > > 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. > > > > > > > I think it's not so much about optimized versus non-optimized at this > > point. It's just that cc/libc memcpy sometimes performs better than > > RTE memcpy, and sometimes doesn't. > > > > For virtio, a single memory copy in > > lib/vhost/virtio_net.c:do_data_copy_enqueue() > > is responsible for >95% of the performance regression introduced by > > the cc memcpy patch for small packets on Intel P-cores. > > > > I'm not so sure this performance regression will go away in newer > > compilers. PGO would certainly help, but PGO is a hassle. > > > > One way to fix this issue would be to introduce a custom, > > memcpy()-based packet copying routine. I tried the below patch, with > > the following results: > > > > Raptor Lake @ 3,2 GHz > > GCC 12 > > > > 64 bytes packets > > Core Mode Mpps > > ---------------------------- > > E RTE memcpy 9.5 > > E cc memcpy 9.7 > > E cc memcpy+pktcpy 9.0 > > > > P RTE memcpy 16.4 > > P cc memcpy 13.5 > > P cc memcpy+pktcpy 16.2 > > > > 1500 bytes > > Core Mode Mpps > > ---------------------------- > > P RTE memcpy 5.8 > > P cc memcpy 5.9 > > P cc memcpy+pktcpy 5.9 > > > > As you can see, most of the regression is eliminated, at the cost of > > worse E-core performance. I didn't look at the generated code, but one > > could suspect heavy use of wide SIMD is to blame, which E-cores don't > > necessarily benefit from. > > > > The below prototype assumes the source and destination buffers are > > 16-byte aligned. Does that always hold? > > Perhaps always for this specific function; I don't know. > Not generally *always*, but I guess in many cases packet copies would have 64-byte aligned pointers, but not sizes. > Unless explicitly stated by the developer, it is unsafe to make assumptions about alignment. > I meant always (for every packet) in DPDK virtio net. > A future rte_memcpy() function might take flags with explicit alignment information for optimized copying, as was part of my non-temporal memcpy(). (The development on this is still on hold.) > There is already a mechanism to express alignment in GCC-compatible compilers. See the below patch. > > > > I'm sure one could further improve performance using context-specific > > information, such as packets always being >= 64 bytes. One could also > > consider having special cases, maybe for 64 bytes and MTU-sized > > packets. Such are always a hassle when you try to characterize > > performance though. > > Absolutely! > > This got me thinking: > These tests are run with 64 byte packets only. > Perhaps branch prediction pollutes the results, by optimizing branches in the copy routine for all packets being 64 byte. > > You really should be testing with IMIX or random packet sizes. > Sure, and it should also be a real app, not testpmd, on top of virtio. > In my experience, most internet packets are large (> 1024 byte, but not 1514 byte due to QUIC's conservative max packet size), closely followed by 64 byte (excl. any VLAN tags) packets; only the minority of packets are medium size. > > > > > diff --git a/lib/vhost/virtio_net.c b/lib/vhost/virtio_net.c > > index 370402d849..7b595a6622 100644 > > --- a/lib/vhost/virtio_net.c > > +++ b/lib/vhost/virtio_net.c > > @@ -231,6 +231,26 @@ vhost_async_dma_check_completed(struct virtio_net > > *dev, int16_t dma_id, uint16_t > > return nr_copies; > > } > > > > +static inline void > > +pktcpy(void *restrict in_dst, const void *restrict in_src, size_t len) > > +{ > > + void *dst = __builtin_assume_aligned(in_dst, 16); > > + const void *src = __builtin_assume_aligned(in_src, 16); > > + > > + if (len <= 256) { > > + size_t left; > > + > > + for (left = len; left >= 32; left -= 32) { > > + memcpy(dst, src, 32); > > + dst = RTE_PTR_ADD(dst, 32); > > + src = RTE_PTR_ADD(src, 32); > > + } > > + > > + memcpy(dst, src, left); > > + } else > > + memcpy(dst, src, len); > > +} > > + > > static inline void > > do_data_copy_enqueue(struct virtio_net *dev, struct vhost_virtqueue > > *vq) > > __rte_shared_locks_required(&vq->iotlb_lock) > > @@ -240,7 +260,7 @@ do_data_copy_enqueue(struct virtio_net *dev, struct > > vhost_virtqueue *vq) > > int i; > > > > for (i = 0; i < count; i++) { > > - rte_memcpy(elem[i].dst, elem[i].src, elem[i].len); > > + pktcpy(elem[i].dst, elem[i].src, elem[i].len); > > vhost_log_cache_write_iova(dev, vq, elem[i].log_addr, > > elem[i].len); > > PRINT_PACKET(dev, (uintptr_t)elem[i].dst, elem[i].len, 0); > > @@ -257,7 +277,7 @@ do_data_copy_dequeue(struct vhost_virtqueue *vq) > > int i; > > > > for (i = 0; i < count; i++) > > - rte_memcpy(elem[i].dst, elem[i].src, elem[i].len); > > + pktcpy(elem[i].dst, elem[i].src, elem[i].len); > > > > vq->batch_copy_nb_elems = 0; > > } > > > > > > > > > Maxime > > >