linux-kernel - using splice/vmsplice to improve file receive performance

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Message-ID: <c70ff3ad0612211121g3c5aaa28s9b738e9c79f9c2be@mail.gmail.com>
Date:	Thu, 21 Dec 2006 21:21:38 +0200
From:	"saeed bishara" <saeed.bishara@...il.com>
To:	linux-kernel@...r.kernel.org, axboe@...e.de
Subject: using splice/vmsplice to improve file receive performance

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 !!
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