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Date: Fri, 28 Dec 2001 09:44:24 -0800 (PST)
From: "Jeffrey W. Baker" <jwb@saturn5.com>
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To: <linux-kernel@vger.kernel.org>
Subject: Re: 2.4.17 absurd number of context switches
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On Fri, 28 Dec 2001, Alan Cox wrote:

> > Check out those figures for context switches!  30,000 switches per second
> > with only three runnable processes and practically no block I/O seems
> > quite high to me.  You can also see that the system is spending half its
> ..
> > Is this a scheduler worst-case, something to be expected, or something I
> > can work around?
>
> The scheduler is _good_ at the three process case. Run some straces it looks
> more like postgres is doing wacky yield based locks.

All I see in strace is semop forever

[pid 10076]      0.000054 semop(1179648, 0xbfffe6e8, 1 <unfinished ...>
[pid 10077]      0.000224 <... semop resumed> ) = 0
[pid 10077]      0.000077 semop(1179648, 0xbfffe1e8, 1) = 0
[pid 10077]      0.000057 semop(1179648, 0xbfffe0f8, 1 <unfinished ...>
[pid 10076]      0.000128 <... semop resumed> ) = 0
[pid 10076]      0.000035 semop(1179648, 0xbfffe6a8, 1) = 0
[pid 10076]      0.000127 semop(1179648, 0xbfffe758, 1 <unfinished ...>
[pid 10077]      0.000085 <... semop resumed> ) = 0
[pid 10077]      0.000075 semop(1179648, 0xbfffe0f8, 1) = 0
[pid 10077]      0.000155 semop(1179648, 0xbfffdfb8, 1 <unfinished ...>
[pid 10076]      0.000401 <... semop resumed> ) = 0
[pid 10076]      0.000034 semop(1179648, 0xbfffe758, 1) = 0
[pid 10076]      0.000046 semop(1179648, 0xbfffe758, 1 <unfinished ...>
[pid 10077]      0.000113 <... semop resumed> ) = 0
[pid 10077]      0.000040 semop(1179648, 0xbfffdf78, 1) = 0
[pid 10077]      0.000051 semop(1179648, 0xbfffdfc8, 1 <unfinished ...>
[pid 10076]      0.000317 <... semop resumed> ) = 0
[pid 10076]      0.000055 semop(1179648, 0xbfffe718, 1) = 0
[pid 10076]      0.000083 semop(1179648, 0xbfffe8d8, 1 <unfinished ...>
[pid 10077]      0.000217 <... semop resumed> ) = 0
[pid 10077]      0.000091 semop(1179648, 0xbfffdfc8, 1) = 0
[pid 10077]      0.000057 semop(1179648, 0xbfffdfa8, 1 <unfinished ...>
[pid 10076]      0.000191 <... semop resumed> ) = 0
[pid 10076]      0.000037 semop(1179648, 0xbfffe898, 1) = 0
[pid 10076]      0.000054 semop(1179648, 0xbfffe928, 1 <unfinished ...>
[pid 10077]      0.000056 <... semop resumed> ) = 0
[pid 10077]      0.000034 semop(1179648, 0xbfffdf68, 1) = 0

-jwb

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