Re: [PATCH 6/9] Include idle and iowait fields in cpuacct
From: Glauber Costa
Date: Tue Sep 20 2011 - 09:29:48 EST
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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