Re: [Patch 6/8] virtual cpu run time

From: Andrew Morton
Date: Thu Mar 30 2006 - 00:02:46 EST


Shailabh Nagar <nagar@xxxxxxxxxxxxxx> wrote:
>
> delayacct-virtcpu.patch
>
> Distinguish between "wall-clock" and "virtual" cpu run times and return
> both, at per-task and per-tgid granularity.
>
> Some architectures adjust tsk->utime+tsk->stime to reflect the time that
> the kernel wasn't scheduled in hypervised environments and this is the
> "wall-clock" cpu run time. "Virtual" cpu run time, on the other hand, does
> not account for the kernel being descheduled.
>
> This patch allows the most accurate "virtual" cpu run time, collected by
> the schedstats code (now shared with delay accounting code), to be returned
> to user space, in addition to the "wall-clock" cpu time that was being exported
> earlier. Both these times are useful for workload management in different
> situations.
>
> In a non-virtualized environment, or on architectures which do not adjust
> tsk->utime/stime, these will effectively be the same value but at different
> granularities.
>
> ...
>
> Index: linux-2.6.16/include/linux/taskstats.h
> ===================================================================
> --- linux-2.6.16.orig/include/linux/taskstats.h 2006-03-29 18:13:18.000000000 -0500
> +++ linux-2.6.16/include/linux/taskstats.h 2006-03-29 18:13:20.000000000 -0500
> @@ -46,8 +46,14 @@ struct taskstats {
> __u64 swapin_count;
> __u64 swapin_delay_total; /* swapin page fault wait*/
>
> - __u64 cpu_run_total; /* cpu running time
> - * no count available/provided */
> + __u64 cpu_run_real_total; /* cpu "wall-clock" running time
> + * Potentially accounts for cpu
> + * virtualization, on some arches
> + */
> + __u64 cpu_run_virtual_total; /* cpu "virtual" running time
> + * Uses time intervals as seen by
> + * the kernel
> + */
> };
>

Again, the reader of this struct wants to know what the atomicity rules are.

> + d->cpu_run_real_total = (tmp < (nsec_t)d->cpu_run_real_total)? 0: tmp;

lval = expr1 ? expr2 : expr3;

> + tmp = (nsec_t)d->cpu_run_virtual_total
> + + (nsec_t)jiffies_to_usecs(t3) * 1000;

umm, Linux doesn't have nsec_t any more.

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