From mboxrd@z Thu Jan 1 00:00:00 1970 From: Yuval Shaia Subject: Re: [PATCH] ib_ipoib: Scatter-Gather support in connected mode Date: Wed, 1 Apr 2015 23:33:15 +0300 Message-ID: <20150401203314.GF8024@yuval-lab> References: <1422357682-8934-1-git-send-email-yuval.shaia@oracle.com> <1422444987.3133.81.camel@opteya.com> <20150201070941.GA4778@yuval-lab> <20150315151616.GA3546@yuval-lab> <20150322092149.GA5229@yuval-lab> <20150323171749.GA3580@obsidianresearch.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20150323171749.GA3580-ePGOBjL8dl3ta4EC/59zMFaTQe2KTcn/@public.gmane.org> Sender: linux-rdma-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Jason Gunthorpe Cc: roland-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org, sean.hefty-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org, hal.rosenstock-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org, linux-rdma-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: linux-rdma@vger.kernel.org On Mon, Mar 23, 2015 at 11:17:49AM -0600, Jason Gunthorpe wrote: > On Sun, Mar 22, 2015 at 11:21:50AM +0200, Yuval Shaia wrote: > > On Sun, Mar 15, 2015 at 05:16:16PM +0200, Yuval Shaia wrote: > > > Hi, > > > I didn't got any further comments on this one. > > > Any idea why SG in CM is un-welcome? > > By mistake I sent a private mail only. > > Cc: Roland Dreier > > Cc: Sean Hefty > > Cc: Hal Rosenstock > > > > Your advice would be very appreciated. > > I haven't looked in detail at the patch, but in principle, using S/G > when ever possible should be the default, even if this creates a > performance regression. Per my testings - no impact on performance. > > It is well known that high order allocations are problematic in Linux > and should be avoided, and I also have seen systems blow up because of > high order IPoIB allocations. Yes, snapshot from oops: Call Trace: [] __alloc_pages_nodemask+0x524/0x595 [] kmem_getpages+0x4f/0xf4 [] fallback_alloc+0x12e/0x1ce [] ____cache_alloc_node+0x121/0x134 [] kmem_cache_alloc_node_notrace+0x84/0xb9 [] __kmalloc_node+0x46/0x73 [] ? __alloc_skb+0x72/0x13d > > That said, there may be cases where S/G is not possible, you should > try and get Mellanox to comment if all their offloads work on all > their cards when S/G is used. Work may be required to resolve any of > these constraints. I'd like to belive there is some reason why we've > been doing high order allocations for so many years. Old kernels (2.6.39) restrict the usage of S/G only to H/W which supports CSUM offload. Mellanox HCA supports CSUM offload only for UD and this is why we can find S/G support for UD but not for CM. With the introduction of commit ec5f061 this limitation is no longer there so no reason not to add this support. > > FWIW, I would probably choose to default S/G over any other offload > acceleration. > > Jason -- To unsubscribe from this list: send the line "unsubscribe linux-rdma" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html