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Date: Fri, 22 Dec 2006 13:18:24 +0200 From: "saeed bishara" <saeed.bishara@...il.com> To: "Jens Axboe" <jens.axboe@...cle.com> Cc: linux-kernel@...r.kernel.org Subject: Re: using splice/vmsplice to improve file receive performance On 12/22/06, Jens Axboe <jens.axboe@...cle.com> 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@...e.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? > > 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? > > -- > Jens Axboe > > View attachment "ttcp.c" of type "text/plain" (17804 bytes) View attachment "splice.h" of type "text/plain" (3448 bytes) Download attachment "Makefile" of type "application/octet-stream" (720 bytes)
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