From: Avi Kivity <avi@redhat.com>
To: Glauber Costa <glommer@redhat.com>
Cc: kvm@vger.kernel.org, zamsden@redhat.com,
Marcelo Tosatti <mtosatti@redhat.com>,
riel@redhat.com
Subject: Re: [RFC 4/7] change kernel accounting to include steal time
Date: Mon, 30 Aug 2010 16:15:04 +0300 [thread overview]
Message-ID: <4C7BAED8.9090409@redhat.com> (raw)
In-Reply-To: <20100830124217.GA17084@mothafucka.localdomain>
On 08/30/2010 03:42 PM, Glauber Costa wrote:
> On Sun, Aug 29, 2010 at 12:59:36PM +0300, Avi Kivity wrote:
>> On 08/26/2010 12:43 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.
>>>
>>> When we do want to register steal time, we proceed as following:
>>> - if we would account user or system time in this tick, and there is
>>> out-of-cpu time registered, we skip it altogether, and account steal
>>> time only.
>>> - if we would account user or system time in this tick, and we got the
>>> cpu for the whole slice, we proceed normaly.
>>> - if we are idle in this tick, we flush out-of-cpu time to give it the
>>> chance to update whatever last-measure internal variable it may have.
>>>
>>> This approach is simple, but proved to work well for my test scenarios.
>>> in a UP guest on UP host, with a cpu-hog in both guest and host shows
>>> ~ 50 % steal time. steal time is also accounted proportionally, if
>>> nice values are given to the host cpu-hog.
>>>
>>> A cpu-hog in the host with no load in the guest, produces 0 % steal time,
>>> with 100 % idle, as one would expect.
>>>
>> The scheduler people and lkml need to be copied on this patch.
>>
>> Since s390 does steal time (I think?), can this code be shared?
> AFAIK, s390 enables CONFIG_VIRT_CPU_ACCOUNTING, so all timings
> comes from the hypervisor, and statistical sampling is not involved.
Ok. I see ppc does something similar as well (taking care of
user/kernel transitions itself).
> We could do that, if our hardware had any method to say precisely
> how much time we spent in each state, which I don't think we do.
We don't, though I'm sure everyone is wondering why we can't have cheap
accurate global clocks on x86.
> So in a summary, s390 is in a totally different ifdef side.
Yes.
> Who should we copy at the scheduler side?
From MAINTAINERS:
Ingo Molnar <mingo@elte.hu>
Peter Zijlstra <peterz@infradead.org>
--
error compiling committee.c: too many arguments to function
next prev parent reply other threads:[~2010-08-30 13:15 UTC|newest]
Thread overview: 40+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-08-25 21:43 [RFC 0/7] KVM steal time implementation Glauber Costa
2010-08-25 21:43 ` [RFC 1/7] Implement getnsboottime kernel API Glauber Costa
2010-08-25 21:43 ` [RFC 2/7] change headers preparing for steal time Glauber Costa
2010-08-25 21:43 ` [RFC 3/7] measure time out of guest Glauber Costa
2010-08-25 21:43 ` [RFC 4/7] change kernel accounting to include steal time Glauber Costa
2010-08-25 21:43 ` [RFC 5/7] kvm steal time implementation Glauber Costa
2010-08-25 21:43 ` [RFC 6/7] touch softlockup watchdog Glauber Costa
2010-08-25 21:43 ` [RFC 7/7] tell guest about steal time feature Glauber Costa
2010-08-26 22:13 ` [RFC 5/7] kvm steal time implementation Rik van Riel
2010-08-26 22:35 ` Glauber Costa
2010-08-26 17:23 ` [RFC 4/7] change kernel accounting to include steal time Marcelo Tosatti
2010-08-26 20:28 ` Glauber Costa
2010-08-26 20:47 ` Marcelo Tosatti
2010-08-26 21:05 ` Rik van Riel
2010-08-26 21:13 ` Glauber Costa
2010-08-26 21:14 ` Anthony Liguori
2010-08-26 21:40 ` Glauber Costa
2010-08-26 23:12 ` Marcelo Tosatti
2010-08-27 0:33 ` Glauber Costa
2010-08-27 15:25 ` Marcelo Tosatti
2010-08-26 21:19 ` Rik van Riel
2010-08-26 21:39 ` Glauber Costa
2010-08-29 9:59 ` Avi Kivity
2010-08-29 15:13 ` Rik van Riel
2010-08-29 15:25 ` Avi Kivity
2010-08-29 15:42 ` Rik van Riel
2010-08-29 15:47 ` Avi Kivity
2010-08-30 12:42 ` Glauber Costa
2010-08-30 13:15 ` Avi Kivity [this message]
2010-08-26 20:54 ` [RFC 3/7] measure time out of guest Zachary Amsden
2010-08-26 21:14 ` Glauber Costa
2010-08-29 9:53 ` Avi Kivity
2010-08-26 20:44 ` [RFC 2/7] change headers preparing for steal time Zachary Amsden
2010-08-26 21:04 ` Rik van Riel
2010-08-26 21:17 ` Glauber Costa
2010-08-26 22:11 ` Rik van Riel
2010-08-29 9:51 ` Avi Kivity
2010-08-30 12:44 ` Glauber Costa
2010-08-30 13:10 ` Avi Kivity
2010-08-26 19:46 ` [RFC 1/7] Implement getnsboottime kernel API Rik van Riel
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