Messages in this thread | | | Date | Tue, 20 Sep 2011 10:29:01 -0300 | From | Glauber Costa <> | Subject | Re: [PATCH 6/9] Include idle and iowait fields in cpuacct |
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On 09/20/2011 10:05 AM, Peter Zijlstra wrote: > On Tue, 2011-09-20 at 09:58 -0300, Glauber Costa wrote: >> On 09/20/2011 09:58 AM, Peter Zijlstra wrote: >>> On Tue, 2011-09-20 at 09:36 -0300, Glauber Costa wrote: >>>> On 09/20/2011 06:21 AM, Peter Zijlstra wrote: >>>>> On Wed, 2011-09-14 at 17:04 -0300, Glauber Costa wrote: >>>>>> These are slightly different from the others though: >>>>>> (note to reviewers: might be better to put those in a separate >>>>>> array?) >>>>>> >>>>>> Since idle/iowait are a property of the system - by definition, >>>>>> no process from any cgroup is running when the system is idle, >>>>>> they are system wide. So what these fields really mean, are baselines >>>>>> for when the cgroup was created. It allows the cgroup to start >>>>>> counting idle/iowait from 0. >>>>> >>>>> Alternatively you can make iowait based on nr_uninterruptible per cgroup >>>>> and count all ticks _this_ cgroup was idle. >>>> You think? >>>> >>>> Humm,humm... maybe... >>>> iowait can indeed be seen as a process group characteristic. I was >>>> mainly concerned about overhead here, specially for the idle case: >>> >>> The overhead of accounting per cgroup nr_uninterruptible is the worst I >>> think, that's in the sleep/wakeup paths. >>> >>>> If we are idle, there is no task context we can draw from, since the >>>> task in the cpu is the idle task. So we end up having to touch all >>>> cgroups... Or am I missing something? >>>> >>>> Sounds expensive. >>> >>> Count the total number of ticks on the cpu (I think we already have >>> that) and subtract the number of ticks in this cgroup (I think we also >>> already have that), which should yield: number of ticks not in this >>> cgroup, aka number of ticks this cgroup was idle. >> No , no... remember steal time. > > Of course I don't.. that's virt stuff, I repress that with all my might. > But add or subtract steal ticks someplace and it doesn't come out right?
That's what I am here for...
But back to your answer:
>>> Count the total number of ticks on the cpu (I think we already have >>> that) and subtract the number of ticks in this cgroup (I think we also >>> already have that),
Not sure if we have ticks in this cgroup... anyway, it can be done. We need a baseline for what was the tick situation when the cgroup started anyway.
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