Namecache lock contention?
Ivan Voras
ivoras at freebsd.org
Fri Jan 28 13:46:25 UTC 2011
I have this situation on a PHP server:
36623 www 1 76 0 237M 30600K *Name 6 0:14 47.27% php-cgi
36638 www 1 76 0 237M 30600K *Name 3 0:14 46.97% php-cgi
36628 www 1 105 0 237M 30600K *Name 2 0:14 46.88% php-cgi
36627 www 1 105 0 237M 30600K *Name 0 0:14 46.78% php-cgi
36639 www 1 105 0 237M 30600K *Name 5 0:14 46.58% php-cgi
36643 www 1 105 0 237M 30600K *Name 7 0:14 46.39% php-cgi
36629 www 1 76 0 237M 30600K *Name 1 0:14 46.39% php-cgi
36642 www 1 105 0 237M 30600K *Name 2 0:14 46.39% php-cgi
36626 www 1 105 0 237M 30600K *Name 5 0:14 46.19% php-cgi
36654 www 1 105 0 237M 30600K *Name 7 0:13 46.19% php-cgi
36645 www 1 105 0 237M 30600K *Name 1 0:14 45.75% php-cgi
36625 www 1 105 0 237M 30600K *Name 0 0:14 45.56% php-cgi
36624 www 1 105 0 237M 30600K *Name 6 0:14 45.56% php-cgi
36630 www 1 76 0 237M 30600K *Name 7 0:14 45.17% php-cgi
36631 www 1 105 0 237M 30600K RUN 4 0:14 45.17% php-cgi
36636 www 1 105 0 237M 30600K *Name 3 0:14 44.87% php-cgi
It looks like periodically most or all of the php-cgi processes are
blocked in "*Name" for long enough that "top" notices, then continue,
probably in a "thundering herd" way. From grepping inside /sys the most
likely suspect seems to be something in the namecache, but I can't find
exactly a symbol named "Name" or string beginning with "Name" that would
be connected to a lock.
Has anyone investigated this before? Any ideas where to look?
The PHP script used above should not do any filesystem writing but it
stats and reads a lot of small files and libraries.
This is 8-stable, UFS.
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