On 03/14/2013 02:43 PM, Zach Brown wrote: >> IIRC, the scheduler timeslice isn't impacted by HZ. > > Yeah. As Dave was pointing out, a lot of the timeout aliasing problems > with HZ have been fixed by moving implementations of waits from the HZ > granular interfaces to hrtimers. f.e. > > commit 8ff3e8e85fa6c312051134b3953e397feb639f51 > Author: Arjan van de Ven <arjan@xxxxxxxxxxxxxxx> > Date: Sun Aug 31 08:26:40 2008 -0700 > > select: switch select() and poll() over to hrtimers > > has at its core: > > - __timeout = schedule_timeout(__timeout); > > + if (!schedule_hrtimeout(to, HRTIMER_MODE_ABS)) > > A slightly different and disappointing result of dropping HZ is > increasing the duration of waits in code that is still using > schedule_timeout(1) for a short timeout. > > btrfs has a bunch of these that are trying to wait for more work to > accumulate before carrying on. If you drop HZ you'll be adding 4ms (or > 10ms) delays to a few paths. > > jbd has similar code that is sensitive to jiffies, but it's a little > more involved because it's measuring journal commit times rather than > using a dumb single jiffie timeout. IOW .. don't modify HZ=1000 yet ;). Durnit ... P. > > Anyway, just a data point. > > - z _______________________________________________ kernel mailing list kernel@xxxxxxxxxxxxxxxxxxxxxxx https://admin.fedoraproject.org/mailman/listinfo/kernel
