Messages in this thread | | | Date | Sat, 11 Apr 2009 12:15:04 -0500 | From | Dimitri Sivanich <> | Subject | Re: [PATCH v2] Move calc_load call out from xtime_lock protection |
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On Sat, Apr 11, 2009 at 06:53:45PM +0200, Thomas Gleixner wrote: > On Sat, 11 Apr 2009, Dimitri Sivanich wrote: > > > On Sat, Apr 11, 2009 at 11:51:36AM +0200, Thomas Gleixner wrote: > > > On Fri, 10 Apr 2009, Dimitri Sivanich wrote: > > > > > > > The xtime_lock is being held for long periods on larger systems due > > > > to an extensive amount of time being spent in calc_load(), > > > > specifically here: > > > > do_timer->update_times->calc_load->count_active_tasks->nr_active() > > > > > > > > On a 64 cpu system I've seen this take approximately 55 usec. > > > > Presumably it would be worse on larger systems. This causes other > > > > cpus to be held off in places such as > > > > scheduler_tick->sched_clock_tick waiting for the xtime_lock to be > > > > released. > > > > > > I thought more about that. Why don't we move the calc_load() call into > > > the timer softirq context and avoid fiddling with all the call sites ? > > > Also moving calc_load out of the timer interrupt context reduces the > > > interrupts off section as well. > > > > > Sounds reasonable to me. > > Ok. I looked once more and I wonder if it's possible to avoid the > whole for_each_online_cpu() business by moving the accounting into the > scheduler and be a bit more clever than just blindly running over all > cpus everytime. > > /me goes back to stare a bit more at the avenrun stuff >
Also, if my patch gets replaced by this, you might want to avoid saving intermediate results in calc_load, as my patch attempts to do.
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