Re: lib/41019: pthreads: high load when using varnish (locking/unlocking causes 98% WCPU)

[Michael Stapelberg <michael+netbsd%stapelberg.de@localhost>]

The following reply was made to PR lib/41019; it has been noted by GNATS.

From: Michael Stapelberg <michael+netbsd%stapelberg.de@localhost>
To: gnats-bugs%NetBSD.org@localhost
Cc: 
Subject: Re: lib/41019: pthreads: high load when using varnish
        (locking/unlocking causes 98% WCPU)
Date: Sun, 15 Mar 2009 22:33:51 +0100

 Hi Andrew,
 
 * [15.03.09 22:26]:
 >  Please ktrace it and provide a kdump snippet.
 kdump consists of *LOTS* of calls like this:
  21193      2 varnishd RET   clock_gettime 0
  21193      2 varnishd CALL  clock_gettime(0,0x7f7ff7bffab0)
  21193      2 varnishd RET   clock_gettime 0
  21193      2 varnishd CALL  clock_gettime(0,0x7f7ff7bffab0)
  21193      2 varnishd RET   clock_gettime 0
  21193      2 varnishd CALL  clock_gettime(0,0x7f7ff7bffab0)
  21193      2 varnishd RET   clock_gettime 0
 
 >  This sleeps for wthread_purge_delay after garbage collecting a thread.
 >  It also sleeps for the same between scans.
 >  What do you have it set to?
 param.show thread_pool_purge_delay
 200 828     
 thread_pool_purge_delay    1000 [milliseconds]
                            Default is 1000
                            Wait this long between purging threads.
                            
                            This controls the decay of thread pools when
                            idle(-ish).
                            
                            Minimum is 100 milliseconds.
                            
                            NB: This parameter may take quite some time to
                            take (full) effect.
                            
                            NB: We do not know yet if it is a good idea to
                            change this parameter, or if the default value is
                            even sensible.  Caution is advised, and feedback
                            is most welcome.
 
 Best regards,
 Michael