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From Brian Pane <bp...@pacbell.net>
Subject Re: load spikes revisited
Date Fri, 18 Jan 2002 06:43:18 GMT
Greg Ames wrote:

>Getting a lot closer.  httpd://www.apache.org/~gregames/ktrace.2_0_28 now has 30
>some seconds of ktrace for comparison purposes.  Interestingly enough, this file
>is considerably smaller than the 2.0.30-dev file which ran for less time. 
>There's about twice the context switches in 2.0.30-dev's ktrace.
>
>prefork was changed to do a apr_poll before the accept, even in the single
>listen case, on Nov 10.  The polls seem to get added to the herd of selects that
>wake up several times a second for no real good reason.  We need to get rid of
>this poll once again.
>

So is the situation basically this:
  * Single listener unserialized accept is enabled on daedalus,
  * We thus have all the idle httpd procs doing a poll before the
    accept,
  * And the spikes in load happen because of the thundering herd
    waking up from the poll when a connection arrives?

If that's the root cause, then I guess 2.0.29 or later with, say,
pthread mutex accept serialization should be able to run without
load spikes on daedalus?

--Brian




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