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From: "Alexander Zagrebin" <alexz@visp.ru>
To: "'Andriy Gapon'" <avg@icyb.net.ua>
References: <3D1C350B94A44E5D95BAA1596D1EBF13@vosz.local><4CCABF73.8070707@icyb.net.ua><F28DAE02F7C94D25B0D86E3D27006C8B@vosz.local>
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Date: Fri, 29 Oct 2010 18:31:21 +0400
Keywords: freebsd-stable
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Cc: freebsd-stable@freebsd.org
Subject: RE: 8.1-STABLE: zfs and sendfile: problem still exists
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> > I've tried the nginx with
> > disabled sendfile (the nginx.conf contains "sendfile off;"):
> > 
> > $ dd if=/dev/random of=test bs=1m count=100
> > 100+0 records in
> > 100+0 records out
> > 104857600 bytes transferred in 5.892504 secs (17795083 bytes/sec)
> > $ fetch -o /dev/null http://localhost/test
> > /dev/null                                     100% of  100 
> MB   41 MBps
> > $ fetch -o /dev/null http://localhost/test
> > /dev/null                                     100% of  100 
> MB   44 MBps
> > $ fetch -o /dev/null http://localhost/test
> > /dev/null                                     100% of  100 
> MB   44 MBps
> > 
> 
> I am really surprised with such a bad performance of sendfile.
> Will you be able to profile the issue further?

Yes.

> I will also try to think of some measurements.

A transfer rate is too low for the _first_ attempt only.
Further attempts demonstrates a reasonable transfer rate.
For example, nginx with "sendfile on;":

$ dd if=/dev/random of=test bs=1m count=100
100+0 records in
100+0 records out
104857600 bytes transferred in 5.855305 secs (17908136 bytes/sec)
$ fetch -o /dev/null http://localhost/test
/dev/null                                       3% of  100 MB  118 kBps
13m50s^C
fetch: transfer interrupted
$ fetch -o /dev/null http://localhost/test
/dev/null                                     100% of  100 MB   39 MBps

If there was no access to the file during some time, then everything
repeats:
The first attempt - transfer rate is too low
A further attempts - no problems

Can you reproduce the problem on your system?

-- 
Alexander Zagrebin