Re: [PATCH 0/2] RFC: readd fair sleepers for server systems
From: Christian Ehrhardt
Date: Wed May 23 2012 - 11:30:40 EST
On 05/23/2012 01:49 PM, Peter Zijlstra wrote:
On Wed, 2012-05-23 at 13:32 +0200, Christian Ehrhardt wrote:
Why is this, is this some weird interaction with your hypervisor?
It is not completely analyzed, as soon as debugging goes out of Linux it
can be kind of complex even internally.
Is there significant steal time in these workloads? If so, does it help
if you implement
CONFIG_PARAVIRT_TIME_ACCOUNTING/paravirt_steal_rq_enabled for s390?
(although I guess we'd better loose the paravirt part of the name then).
Interesting, yeah there is enough steal time - not in all, but in most
cases we had in conflict with fair sleepers so far.
We don't have any code for CONFIG_PARAVIRT and its childs yet, so I need
to look further into it.
This 'feature' subtracts steal time from the task-clock so that the
scheduler doesn't consider a task to be running when the vcpu wasn't
running as well.
Not doing that (current situation) could result in over-active
preemption because we think a task ran significantly longer than it
actually did. Same for sleeper fairness, we might think a task slept
very long (and give a bigger boost) when in fact it didn't.
Great - sounds like a good thing to check, I'll definitely try this out.
This week we are changing our automation environment, so give me a few
days for numbers on that.
--
GrÃsse / regards, Christian Ehrhardt
IBM Linux Technology Center, System z Linux Performance
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