linux-kernel - Re: [PATCH 1/9] perf_counter: unify and fix delayed counter wakeup

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Message-ID: <18895.18217.393755.824092@cargo.ozlabs.ibm.com>
Date:	Sun, 29 Mar 2009 21:02:17 +1100
From:	Paul Mackerras <paulus@...ba.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org,
	Mike Galbraith <efault@....de>,
	Arjan van de Ven <arjan@...radead.org>,
	Wu Fengguang <fengguang.wu@...el.com>,
	Eric Dumazet <dada1@...mosbay.com>
Subject: Re: [PATCH 1/9] perf_counter: unify and fix delayed counter wakeup

Peter Zijlstra writes:

> In a perfect world, I'd introduce a self-ipi on UP and use that. Also,
> in that same perfect world, all arches would support cmpxchg()/xchg() so
> we could put the whole thing in generic code.

We already require atomic64_t, which not all architectures have - in
particular, ppc32 doesn't have it, though it does have cmpxchg/xchg
for 32-bit quantities.  The list of architectures that have atomic64_t
seems to be a proper subset of the list of architectures that have
cmpxchg, from a quick grep.  So I would think you can use cmpxchg if
necessary.

Paul.
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