From mboxrd@z Thu Jan 1 00:00:00 1970 From: Christoph Hellwig Subject: Re: [PATCH 0/5] Indirect memory registration feature Date: Mon, 8 Jun 2015 06:51:51 -0700 Message-ID: <20150608135151.GA14021@infradead.org> References: <1433769339-949-1-git-send-email-sagig@mellanox.com> <20150608132254.GA14773@infradead.org> <55759B0B.8050805@mellanox.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <55759B0B.8050805-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org> Sender: linux-rdma-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Sagi Grimberg Cc: Christoph Hellwig , Doug Ledford , linux-rdma-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Or Gerlitz , Eli Cohen , Oren Duer , Sagi Grimberg List-Id: linux-rdma@vger.kernel.org On Mon, Jun 08, 2015 at 04:39:23PM +0300, Sagi Grimberg wrote: > I have learned about QUEUE_FLAG_SG_GAPS from your recent comments on > the list. Won't setting this flag interfere with bio merges? It would if any in-kernel consumer would actually generate such SG lists. But none does - the only source is vectored SG_IO support. > Ideally > I wouldn't want to restrict merges if my device supports this feature. > > >Right now drivers tat set these would always fail SG_IO ioctls using > >iovecs, but that can be fixed much more easily by doing high level > >bounce buffering compared to these horrible workarounds deep down in the > >stack. > > > > My tests have shown significant cpu savings with this against SW bounce > buffering, especially for large transfers. I've seen applications that > a significant part of their IO workload consists of this type of memory > layout. > > I must say that I've always considered SW bounce buffering as a > work-around for an RDMA driver. bounce buffering is always a workaround, and offloading it to silicone just makes it a worse hack. So please fix it in the proper layers first, and if you really care about the vectored SG_IO case use your indirect registrations just for that. -- 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