Timers and timing, was: MySQL Performance 6.0rc1

David Xu 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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