Re: [RFC v2 4/7] change kernel accounting to include steal time

[Rik van Riel <riel@redhat.com>]

On 08/30/2010 01:30 PM, Jeremy Fitzhardinge wrote:
>   On 08/30/2010 09:06 AM, Glauber Costa wrote:
>> This patch proposes a common steal time implementation. When no
>> steal time is accounted, we just add a branch to the current
>> accounting code, that shouldn't add much overhead.
>
> How is stolen time logically any different from a CPU running slowly due
> to HT or power management?  Is it worth trying to handle them in the
> same way?  (I'm mostly picking on the "_from_hypervisor" part, since
> that seems over-specific.)
>
> Why not have a get_unstolen_time() function which just returns
> sched_clock() in the normal case, but can return less?

Steal time gets you information you can act on, when
your program is running slowly.

The steal time statistic allows you to see whether the
slowdown was due to the CPU just not being fast enough,
or due to something else contending for the CPU.

This can be useful information. Apparently, it has been
useful enough that it has been implemented on s390, PPC
and Xen (pre pvops Xen).

I suppose HT can have similar results, but that is
also something that system administrators can see.

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