On Tue, 2013-05-28 at 20:30 +0200, Florian Weimer wrote: > On 05/28/2013 08:09 PM, Václav Zeman wrote: > > > If the bottleneck is really in glibc, then you should probably ask them > > to fix it. Could the mutex be changed rwlock instead? > > rwlocks don't eliminate hardware contention, so I doubt they'd be a win > here.
Indeed. Reader-writer locks guarantee the critical section, even the readers, that they run mutually exclusive with writers. So whatever you do while holding the lock, the protected data won't change. That restricts what we can do, because we need to actively prevent writers from doing things, which means making your read operation visible to others (unless you can stop the writers in some other funny ways). However, we only seem to need an atomic snapshot here AFAIU, in which case we can do stuff like reading the data optimistically, verifying that we read consistent data, and retrying if we didn't.
