Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754820AbWLVMpS (ORCPT ); Fri, 22 Dec 2006 07:45:18 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754821AbWLVMpS (ORCPT ); Fri, 22 Dec 2006 07:45:18 -0500 Received: from brick.kernel.dk ([62.242.22.158]:1892 "EHLO kernel.dk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754820AbWLVMpR (ORCPT ); Fri, 22 Dec 2006 07:45:17 -0500 Date: Fri, 22 Dec 2006 13:47:11 +0100 From: Jens Axboe To: saeed bishara Cc: linux-kernel@vger.kernel.org Subject: Re: using splice/vmsplice to improve file receive performance Message-ID: <20061222124710.GR17199@kernel.dk> References: <20061222094858.GP17199@kernel.dk> <20061222113917.GQ17199@kernel.dk> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3957 Lines: 89 On Fri, Dec 22 2006, saeed bishara wrote: > On 12/22/06, Jens Axboe wrote: > >On Fri, Dec 22 2006, saeed bishara wrote: > >> On 12/22/06, Jens Axboe wrote: > >> >On Thu, Dec 21 2006, saeed bishara wrote: > >> >> Hi, > >> >> I'm trying to use the splice/vmsplice system calls to improve the > >> >> samba server write throughput, but before touching the smbd, I started > >> >> to improve the ttcp tool since it simple and has the same flow. I'm > >> >> expecting to avoid the "copy_from_user" path when using those > >> >> syscalls. > >> >> so far, I couldn't make any improvement, actually the throughput get > >> >> worst. the new receive flow looks like this (code also attached): > >> >> 1. read tcp packet (64 pages) to page aligned buffer. > >> >> 2. vmsplice the buffer to pipe with SPLICE_F_MOVE. > >> >> 3. splice the pipe to the file, also with SPLICE_F_MOVE. > >> >> > >> >> the strace shows that the splice takes a lot of time. also when > >> >> profiling the kernel, I found that the memcpy() called to often !! > >> > > >> >(didn't see this until now, axboe@suse.de doesn't work anymore) > >> > > >> >I'm assuming that you mean you vmsplice with SPLICE_F_GIFT, to hand > >> >ownership of the pages to the kernel (in which case SPLICE_F_MOVE will > >> >work, otherwise you get a copy)? If not, that'll surely cost you a data > >> >copy > >> I'll try the vmplice with SPLICE_F_GIFT and splice with MOVE. btw, > >> I noticed that the splice system call takes the bulk of the time, > >> does it mean anything? > > > >Hard to say without seeing some numbers :-) > I'm out of the office, I'll send it later. btw, my test bed ( the > receiver side ) is arm9. does it matter? The vmsplice is basically vm intensive, so it could matter. > >> >This sounds remarkably like a recent thread on lkml, you may want to > >> >read up on that. Basically using splice for network receive is a bit of > >> >a work-around now, since you do need the one copy and then vmsplice that > >> >into a pipe. To realize the full potential of splice, we first need > >> >socket receive support so you can skip that step (splice from socket to > >> >pipe, splice pipe to file). > >> Ashwini Kulkarni posted patches that implements that, see > >> http://lkml.org/lkml/2006/9/20/272 . is that right? > >> > > >> >There was no test code attached, btw. > >> sorry, here it is. > >> can you please add sample application to your test tools (splice,fio > >> ,,) that demonstrates my flow; socket to file using read & vmsplice? > > > >I didn't add such an example, since I had hoped that we would have > >splice from socket support sooner rather than later. But I can do so, of > >course. > do you any preliminary patches? I can start playing with it. I don't, Intel posted a set of patches a few months ago though. I didn't have time to look that at the time being, but you should be able to find them in the archives. > >I'll try your test. One thing that sticks out initially is that you > >should be using full pages, the splice pipe will not merge page > >segments. So don't use a buflen less than the page size. > > yes, actually I run the ttcp with -l65536 ( 64KB ), and the buffer is > always page aligned.also, the splice/vmsplice with MOVE or GIFT will > fail if the buffer is not a whole pages. am I rigth? Yes. I added a simple splice-fromnet example in the splice git repo, see if you can repeat your results with that. Doing: # ./splice-fromnet -g 2001 | ./splice-out -m /dev/null and # cat /dev/zero | netcat localhost 2001 gets me about 490MiB/sec, using a recv/write loop is around 413MiB/sec. Not migrating pages gets me around 422MiB/sec. -- Jens Axboe - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/