linux-kernel - Re: [PATCH 09/11] x86, perf: Support sysfs files depending on SMT status

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Message-ID: <20160118222832.GK4698@two.firstfloor.org>
Date:	Mon, 18 Jan 2016 23:28:32 +0100
From:	Andi Kleen <andi@...stfloor.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Andi Kleen <andi@...stfloor.org>, acme@...nel.org,
	jolsa@...nel.org, eranian@...gle.com, linux-kernel@...r.kernel.org,
	mingo@...nel.org, Andi Kleen <ak@...ux.intel.com>
Subject: Re: [PATCH 09/11] x86, perf: Support sysfs files depending on SMT
 status

> So one obvious problem with this is that a concurrent hotplug operation
> can toggle ht_on resulting in bogus measurements.
> 
> I'm not sure there's anything we can do about that, other than WARN in
> the tool if it finds inconsistent results; does it?

Right. Supporting a good interface for user programs to be informed
of CPU hotplug would be useful for a lot of things, but currently
it doesn't exist and it's definitely outside the scope of this
patchkit. If such an interface existed perf stat could use it
to reconfigure itself.

It's hard to do a good sanity check unfortunately.

-Andi

-- 
ak@...ux.intel.com -- Speaking for myself only.