Timers and timing, was: MySQL Performance 6.0rc1
davidxu at freebsd.org
Fri Oct 28 18:09:27 PDT 2005
Robert Watson wrote:
> Another important question is whether using these alternative time
> access methods in user space improves the performance of any of the
> applications we care about. Hence providing a patch that someone can
> try -- while the microbenchmarks seem to show improved performance,
> will the applications? I suspect it will in some important cases, but
> there's only one way to find out.
> It strikes me that replacing time(3) with something that retrieves
> CLOCK_SECOND shouldn't harm time(3) semantics. Likewise, keeping
> CLOCK_REALTIME as is is likely OK -- if an application requests it
> using clock_gettime(), then it is presumably looking for high
> accuracy. It's gettimeofday() that's the troubling one -- it's widely
> used to query the time in applications, and its API suggests
> microsecond resolution.
> Robert N M Watson
thread libraries use clock_gettime, this becauses there is
pthread_cond_timedwait and other synchronization objects
like rwlock, and mutex all have a timeout version, I think
pthread_cond_timedwait is mostly used in some applications,
though normally, application is not looking for high accuracy.
they will get benefit from the clock_gettime speed improvement.
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