Messages in this thread | ![/](/images/icornerl.gif) | | Date | Mon, 22 Dec 2003 09:48:24 +0100 | From | Ingo Molnar <> | Subject | Re: 2.6 vs 2.4 regression when running gnomemeeting |
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* Christian Meder <chris@onestepahead.de> wrote:
> > nice -19 ./loop & > > > > do a couple of such loops still degrade gnomemeeting? > > I found the culprit. It's sched_yield again. When I straced > gnomemeeting even without load I saw a lot of sched_yields. [...]
this is definitely broken code. Such code already causes big CPU overhead in certain circumstances (under 2.4 too) - but in 2.6 it also shows up as an interactivity problem. So 2.4 hid the problem, 2.6 exposes it.
> So the questionable code in pwlib is probably:
> > BOOL PSemaphore::Wait(const PTimeInterval & waitTime)
yeah. pwlib should be fixed. The quick fix is, instead of sched_yield(), to do:
{ struct timespec timer = { 0, 1 };
nanosleep (&timer, NULL); }
this does what pwlib really wants to do: sleep for the shortest amount of time posssible, because its semaphore implementation is polling based.
(but pwlib should perhaps use sem_timedwait(sem, abs_timeout) instead - which does exactly what PSemaphore::Wait() tries to implement.)
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