linux-kernel - Re: [PATCH v1] sched: fix nohz idle load balancer issues

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Date:	Tue, 27 Sep 2011 16:01:06 +0530
From:	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Paul Turner <pjt@...gle.com>,
	Venki Pallipadi <venki@...gle.com>,
	Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>,
	Kamalesh Babulal <kamalesh@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1] sched: fix nohz idle load balancer issues

* Ingo Molnar <mingo@...e.hu> [2011-09-27 08:32:24]:

> What are the tasks doing which are running - are they plain burning 
> CPU time? If the tasks do something more complex, do you also have a 
> measure of how much work gets done by the workload, per second?

They are simple cpu hogs at this time.

> Percentual changes in that metric would be nice to include in an 
> additional column - that way we can see that it's not only idle
> that has gone down, but workload performance has gone up too.

Ok, good point.

> In fact even if there was only a CPU burning loop in the workload it 
> would be nice to make that somewhat more sophisticated by letting it 
> process some larger array that has a cache footprint. This mimics 
> real workloads that don't just spin burning CPU time but do real data 
> processing.
> 
> For any non-trivial workload it's possible to reduce idle time 
> without much increase in work done and in fact it's possible to 
> decrease idle time *and* work done - so we need to see more clearly 
> here and make sure it's all an improvement.

Ok - I will run a cpu intensive benchmark and get some numbers on
how benchmark score varies with the patch applied. I can pick a simple
matrix multiplication type benchmark, unless you have other suggestions!

- vatsa
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