linux-kernel - Re: [PATCH v2 5/7] ARM: perf_event: Fully support Krait CPU PMU events

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Message-ID: <20140123103216.GC5466@mudshark.cambridge.arm.com>
Date:	Thu, 23 Jan 2014 10:32:16 +0000
From:	Will Deacon <will.deacon@....com>
To:	Stephen Boyd <sboyd@...eaurora.org>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-msm@...r.kernel.org" <linux-arm-msm@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Neil Leeder <nleeder@...eaurora.org>,
	Ashwin Chaugule <ashwinc@...eaurora.org>
Subject: Re: [PATCH v2 5/7] ARM: perf_event: Fully support Krait CPU PMU
 events

On Wed, Jan 22, 2014 at 08:47:58PM +0000, Stephen Boyd wrote:
> On 01/21/14 10:37, Stephen Boyd wrote:
> > On 01/21/14 10:07, Will Deacon wrote:
> >> Do you need isbs to ensure the pmresrn side-effects have happened, or are
> >> the registers self-synchronising? Similarly for your other IMP DEF
> >> registers.
> > There aren't any isbs in the downstream android sources so I assume
> > they're self synchronizing. I'll confirm with the CPU designers to make
> > sure.
> >
> 
> CPU folks say no need for isb.

Good, good!

> They mentioned that the lack of an isb after the
> armv7_pmnc_enable_counter() call will leave the action of enabling the
> counter "in-flight". The window is probably pretty short on an SMP kernel
> because of the spin_unlock right after with the barriers in it, but the
> same can't be said for a UP kernel.

Yep, we rely on the exception return for that.

> Also, the fuzzer didn't find anything else, but I found a bug in the
> bitmap logic, updated and reran the fuzzer this morning. Everything
> looks good.

Okey doke, I guess if you can repost at -rc1 then I can look at pulling
this into my tree.

Cheers,

Will
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