linux-kernel - Re: [RFC PATCH 2/4] x86, mwaitt: introduce mwaitx idle with a configurable timer

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Message-ID: <20150521160223.GA23652@pd.tnic>
Date:	Thu, 21 May 2015 18:02:23 +0200
From:	Borislav Petkov <bp@...e.de>
To:	Huang Rui <ray.huang@....com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>,
	Ingo Molnar <mingo@...nel.org>, Len Brown <lenb@...nel.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	"x86@...nel.org" <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Fengguang Wu <fengguang.wu@...el.com>,
	Aaron Lu <aaron.lu@...el.com>, "Li, Tony" <Tony.Li@....com>,
	Frédéric Weisbecker <fweisbec@...il.com>,
	Andy Lutomirski <luto@...capital.net>
Subject: Re: [RFC PATCH 2/4] x86, mwaitt: introduce mwaitx idle with a
 configurable timer

On Thu, May 21, 2015 at 10:56:32PM +0800, Huang Rui wrote:
> Looks like good use case. Boris, could we try to implement it?

Andy had some suggestions on how to do it here:

https://lkml.kernel.org/r/555D3629.8080002@kernel.org

which should be doable. Also, you'd probably need to set ECX[0]=0b too,
so that MWAITX doesn't get woken up by interrupts while MWAIT-ing with
interrupts disabled. I.e., this sequence:

cli
rdtsc
shove the computed timeout into ebx
mov $2,%ecx				# this enables the timer and disables IRQs while MWAITing
mwaitx
sti

The NMI argument is a problem though - if and NMI gets you out of
MWAITX, a simple perf tool workload would kill all MWAITX executions.
Which is bad. :-\

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
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