linux-kernel - Re: [PATCH 1/1] perf/x86/intel/uncore: Add support for Intel SKL client uncore

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Message-ID: <20160420163422.GA19706@tassilo.jf.intel.com>
Date:	Wed, 20 Apr 2016 09:34:22 -0700
From:	Andi Kleen <ak@...ux.intel.com>
To:	"Liang, Kan" <kan.liang@...el.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	"peterz@...radead.org" <peterz@...radead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"eranian@...gle.com" <eranian@...gle.com>
Subject: Re: [PATCH 1/1] perf/x86/intel/uncore: Add support for Intel SKL
 client uncore

> Right. How about check the SKL_UNC_PERF_GLOBAL_CTL in enable_event?
> If it's cleared, we can reset it there. The drawback is that there will be an extra
> rdmsrl and a possible wrmsrl. 

It's better to not rely on register state for this. There are a variety
of user space tools that manipulate the uncore MSRs through /dev/*/msr
So better keep software state. Software state is also much faster than
reading MSRs.

-Andi

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