Hi!
> We just want to avoid the stupidity of dropping down the frequency to a
> minimum
> and then enduring a needless (and long) delay before ramping it up back again.
> So, let us simply carry forward the previous load - that is, let us just
> pretend
> that the 'load' for the current time-window is the same as the load for the
> previous window. That way, the frequency and voltage will continue to be set
> to whatever values they were set at previously. This means that bursty
> workloads
> will get a chance to influence the CPU frequency at which they wake up from
> cpu-idle, based on their past execution history. Thus, they might be able to
> avoid suffering from slow wakeups and long response-times.
>
> [ The right way to solve this problem is to teach the CPU frequency governors
> to track load on a per-task basis, not a per-CPU basis, and set the
> appropriate
> frequency on whichever CPU the task executes. But that involves redesigning
> the cpufreq subsystem, so this patch should make the situation bearable until
> then. ]
Are you sure? For example "./configure" load consists of a lot of
short-lived tasks. Per-task basis may not be option for that.
> A rudimentary and somewhat approximately latency-sensitive workload such as
> sleeping-ebizzy itself showed a consistent, noticeable performance improvement
> with this patch. Hence, workloads that are truly latency-sensitive will
> benefit
> quite a bit from this change. Moreover, this is an overall win-win since this
> patch does not hurt power-savings at all (because, this patch does not reduce
> the idle time or idle residency; and the high frequency of the CPU when it
> goes
> to cpu-idle does not affect/hurt the power-savings of deep idle
> states).
Are you sure about win-win?
AFAICT, your patch helps
##########.........#########.........###########...........##########............
case (not surprising, that's why you wrote the patch :-), but what happens in
##########.........#.................#.....................#.....................
case? (That is idle system, with some tasks taking very small ammounts
of CPU).
AFAICT, it will remember the (high) prev_load over the idle period,
and use too high frequency for mostly idle system, no?
Pavel
--
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures)
http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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