On Wed, Aug 19, 2009 at 3:54 AM, Poul-Henning Kamp<[email protected]> wrote: > In message <[email protected]>, Mark > M > oseley writes: >>I've seen various things in the wiki and threads on this list talking >>about thread pools. In general, the advice is typically conservative, >>i.e. don't use more than the default 2 thread pools unless you have >>to. I've also seen the occasional comment suggesting one run as many >>thread pools as there are cores/cpus. > > I think the point here is "don't make 1000 or even 100 pools". > > One pool per core should be all you need to practically eliminate > thread contention, but to truly realize this, we would have to pin > pools on cores and other nasty and often backfiring "optimizations". > > Having a few too many pools probably does not hurt too much, but > may increase the thread create/kill ratio a bit. > >>Also, the wiki mentions that it's mainly appropriate when you run into >>locks tying things up. Is that mainly a case of high LRU turnover or >>are there other scenarios where locking is an issue? What are the >>symptoms of locking becoming an issue with the current configuration >>and what fields in varnishstat should I be looking at? > > POSIX unfortunately does not offer any standard tools for analysing > lock behaviour, so we have had to make some pretty crude ones > ourselves. > > The main sign of lock issues is that the number of context switches > increase drastically, you OS can probably give you a view of that > number. > > If you want to go deeper, we have a flag in diag_bitmaps that enables > shmlogging of lock contentions (or even all lock operations), together > with varnishtop suitably filtered, that gives a good idea which locks > we have trouble with. > >>but I worry about wasting any CPU% on those 8 core 1950s [...] > > Varnish is all about wasting CPU%, normally we barely touch the > CPUs, man systems running with 80-90% idle CPUs. > > Have you played a bit with varnihshist ? I suspect that may be > the most sensitive, if crude, indicator of overall performance > we can offer.
This is all excellent info, lots to chew on. Thanks! I've stared at varnishhist a number of times and both our hits and misses are showing up in pretty expected places. _______________________________________________ varnish-misc mailing list [email protected] http://projects.linpro.no/mailman/listinfo/varnish-misc
