linux-kernel - Re: cli/sti vs local_cmpxchg and local_add_return

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Message-ID: <20090317193532.GA18503@Krystal>
Date:	Tue, 17 Mar 2009 15:35:32 -0400
From:	Mathieu Desnoyers <compudj@...stal.dyndns.org>
To:	David Miller <davem@...emloft.net>
Cc:	ltt-dev@...ts.casi.polymtl.ca, mingo@...e.hu,
	paulmck@...ux.vnet.ibm.com, jwboyer@...ux.vnet.ibm.com,
	linux-kernel@...r.kernel.org
Subject: Re: cli/sti vs local_cmpxchg and local_add_return

* David Miller (davem@...emloft.net) wrote:
> From: Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
> Date: Tue, 17 Mar 2009 12:06:35 -0400
> 
> > But powerpc has non-maskable interrupts, so for less than 4 cycles, I
> > think it's better to stay with the local_t variant to be NMI-safe.
> 
> Sparc64 has non-maskable interrupts too btw.
> 

OK, this alone is a strong argument to favor NMI-safe lockless algorithm
even if it is a bit slower. We should see what kind of performance
impact it has on overall tracing performance to find out if it will make
a measurable difference anyway.

Mathieu

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Mathieu Desnoyers
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