> 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.
Anyway, just a data point.
- z
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