linux-kernel - Re: [RFC][PATCH 0/8] load-balancing and cpu

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Date:	Thu, 3 Sep 2009 14:10:45 +0200
From:	Andreas Herrmann <andreas.herrmann3@....com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
CC:	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org,
	Gautham R Shenoy <ego@...ibm.com>,
	Balbir Singh <balbir@...ibm.com>
Subject: Re: [RFC][PATCH 0/8] load-balancing and cpu_power -v2

On Tue, Sep 01, 2009 at 10:34:31AM +0200, Peter Zijlstra wrote:
> A more complete version, one that compiles and mostly works on the
> simple tests to which it was subjected.
> 
> It still lacks integration with APERF/MPERF because that stuff was
> hidding in some acpi driver instead of placed in arch code for general
> consumption.. will fix.
> 
> Also, SD_SHARE_CPUPOWER seems redundant in the face of sd->level ==
> SD_LV_SIBLING, should we remove the SD_flag or depricate the level?
> 
> Anyway, have at it, poke holes and report issues.

Tested it (to a certain extend).
Found no performance degradation (on 1P, 2P, 4P systems). (One could
think performance might slightly degrade due to more frequent
__cpu_power updates).

Issue that I see is that switching between scheduling policies has no
effect on already running tasks:

- tasks that are already distributed among sockets are _not_
  concentrated on one socket when switching from performance to
  power_savings scheduling

- tasks utilizing a socket are _not_ distributed among sockets when
  switching from power_savings to performance policy

This applies to modification of sched_mc_power_savings. And I think
one of above scenarios is already broken in tip/master w/o your
patches.

Otherwise especially wrt to integration of APERF/MPERF this seems to
be a good approach.


Regards,
Andreas

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