Subject: Re: 3.0.1: softdep + ffsv2 + 'heavy' load = pauses
To: Mark Cullen <>
From: Greg A. Woods <>
List: netbsd-users
Date: 07/21/2006 13:40:31
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At Fri, 21 Jul 2006 15:16:57 +0100,
Mark Cullen wrote:
> The solution, so far, appears to be to just turn off softdep. I'm
> seeing no pauses now with either of the tests, SSH on the dbench test
> logs in nice and quick.. as if the machine were still idle! Though I
> am sure turning off softdep has a horrible performance impact, so I
> would really like to use it.

Why don't you actually measure the final system throughput with and
without softdep?  I.e. time the start to completion of the whole test,
once with softdep and once without.  Don't do _anything_ else on the
system while running these tests.  Do them in single user mode if
possible (run "/etc/rc.d/network start" and _only_ whatever else is
needed to get NFS running for the NFS test).

> On a side note, I tried running `dbench` on the home server with just
> 20 clients and it totally hung the machine when it got to the
> "executing" stage of the test. I'm not terribly sure why either.

You need to pay very close attention to how all your system's resources
are being used during such tests.  Run trials with fewer jobs and see
how well things are behaving.  You'll probably need to run several
trials and each time run top, then various systat views, then maybe
iostat and maybe vmstat.  Watch how each resource is utilized.  Try to
figure out which resource is being exhausted, if indeed that's the cause
of the hang.  If you can't identify an obvious thing like RAM or CPU or
I/O channels then it's probably some less easy to see internal kernel
resource -- perhaps some table filling up or whatever.  That's where
kernel debuggers come in very handy.

						Greg A. Woods

H:+1 416 218-0098 W:+1 416 489-5852 x122 VE3TCP RoboHack <>
Planix, Inc. <>       Secrets of the Weird <>

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