Messages in this thread | | | Date | Fri, 12 Jun 2009 13:20:08 +0200 | From | Stanislaw Gruszka <> | Subject | Re: [RFC PATCH] posix-cpu-timers: optimize calling thread_group_cputime() |
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On Fri, 12 Jun 2009 13:09:46 +0200 Peter Zijlstra <a.p.zijlstra@chello.nl> wrote:
> On Fri, 2009-06-12 at 12:39 +0200, Stanislaw Gruszka wrote: > > - times->utime = cputime_add(times->utime, t->utime); > > - times->stime = cputime_add(times->stime, t->stime); > > - times->sum_exec_runtime += t->se.sum_exec_runtime; > > + if (mask & TG_CPUCLOCK_UTIME) > > + times->utime = cputime_add(times->utime, t->utime); > > + if (mask & TG_CPUCLOCK_STIME) > > + times->stime = cputime_add(times->stime, t->stime); > > + if (mask & TG_CPUCLOCK_SCHED) > > + times->sum_exec_runtime += t->se.sum_exec_runtime; > > Does adding 3 branches really make it faster? Actually I did not any benchmarking yet, so I don't know what is the real impact of the patch. I hope it make things taster but the result can be opposite from my expectations.
> Since you're bound to want > at least one, I would expect the cacheline to be hot (assuming all three > variables live in the same cacheline -- if not, they should be!), so all > you're avoiding is the addition.
utime, stime are probable in the same cache line, se.sum_exec_runtime is far away from them in struct task_struct so it's in rather separate cache line.
Stanislaw
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