linux-kernel - Re: local64_cmpxchg() in arc_perf_event

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Message-ID: <20151117110749.GT3816@twins.programming.kicks-ass.net>
Date:	Tue, 17 Nov 2015 12:07:49 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Vineet Gupta <Vineet.Gupta1@...opsys.com>
Cc:	Alexey Brodkin <Alexey.Brodkin@...opsys.com>,
	arcml <linux-snps-arc@...ts.infradead.org>,
	lkml <linux-kernel@...r.kernel.org>
Subject: Re: local64_cmpxchg() in arc_perf_event_update()

On Tue, Nov 17, 2015 at 09:14:59AM +0000, Vineet Gupta wrote:
> Let's check with Peter as I'm not sure how exactly the read call will
> nest for same counter on same core ?

Various possible ways, but the easiest is userspace doing a sys_read()
on the counter while the NMI happens.


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