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From: "H. Peter Anvin" <hpa@zytor.com>
To: Venki Pallipadi <venkatesh.pallipadi@intel.com>
Cc: Ingo Molnar <mingo@elte.hu>, Thomas Gleixner <tglx@linutronix.de>,
	linux-kernel <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] x86: Add clflush before monitor for Intel 7400 series
Date: Tue, 07 Oct 2008 14:09:12 -0700	[thread overview]
Message-ID: <48EBCFF8.6050500@zytor.com> (raw)
In-Reply-To: <20081007210056.GA5802@linux-os.sc.intel.com>

Venki Pallipadi wrote:
> For Intel 7400 series CPUs, the recommendation is to use a clflush on the
> monitored address just before monitor and mwait pair [1]. This clflush makes
> sure that there are no false wakeups from mwait when the monitored address
> was recently written to.
> 
> [1] "MONITOR/MWAIT Recommendations for Intel Xeon Processor 7400 series"
> section in specification update document of 7400 series
> http://download.intel.com/design/xeon/specupdt/32033601.pdf
> 
> Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>

This seems very expensive.  It really makes me wonder if it wouldn't 
just be better to either declare monitor/mwait non-functional on this 
chip, or make sure that mwaits can handle false wakeups.

	-hpa

  reply	other threads:[~2008-10-07 21:10 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-10-07 21:00 [PATCH] x86: Add clflush before monitor for Intel 7400 series Venki Pallipadi
2008-10-07 21:09 ` H. Peter Anvin [this message]
2008-10-07 21:49   ` Venki Pallipadi
2008-10-07 23:02     ` H. Peter Anvin
2008-10-17 20:05       ` Pallipadi, Venkatesh
2008-10-17 20:13         ` H. Peter Anvin
2008-10-17 20:51           ` Pallipadi, Venkatesh
2008-10-17 22:49             ` H. Peter Anvin
2008-10-18  7:15               ` Andi Kleen

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