[lkml]   [2006]   [Jun]   [9]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: [ckrm-tech] [RFC 0/4] sched: Add CPU rate caps (improved)
Peter Williams wrote:
> I've done some informal testing with smaller values of CAP_STATS_OFFSET
> and there is only a minor improvement.
> However, something that does improve behaviour for short lived tasks is
> to increase the value of HZ. This is because the basic unit of CPU
> allocation by the scheduler is 1/HZ and this is also the minimum time
> (and granularity) with which sinbinning and other capping measures can
> be implemented. This is the fundamental limiting factor for the
> accuracy of capping i.e. if everything worked perfectly the best
> granularity that can be expected from capping of short lived tasks is
> 1000 / (HZ * duration) where duration is in seconds.

I already defines CONFIG_HZ=1000. Do you suggest increasing more?

> For longer living tasks, once the initial phase has passed the half life
> of the Kalman filters takes over from "HZ * duration" in the above
> expression. Reducing CAP_STATS_OFFSET will shorten the half life of the
> filters and this in turn will make capping coarser. On the other hand,
> if the half lives are too big then capping will be too slow in reacting
> to changes in a task's CPU usage patterns. So there's a sweet spot in
> there somewhere. There's also an upper limit imposed by the likelihood
> of arithmetic overflow during the calculations and this has to consider
> the fact that the average cycle length (one of the metrics) can be quite
> long. The current values was based on these considerations.
> Peter

MAEDA Naoaki

To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to
More majordomo info at
Please read the FAQ at

 \ /
  Last update: 2006-06-09 07:53    [W:0.048 / U:8.620 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site