linux-kernel - Re: [PATCH 1/6] x86-mce: Modify CMCI poll interval to adjust for small check

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Message-ID: <20140710090150.GB10182@gchen.bj.intel.com>
Date:	Thu, 10 Jul 2014 05:01:51 -0400
From:	"Chen, Gong" <gong.chen@...ux.intel.com>
To:	Havard Skinnemoen <hskinnemoen@...gle.com>
Cc:	Borislav Petkov <bp@...en8.de>, Tony Luck <tony.luck@...el.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Ewout van Bekkum <ewout@...gle.com>
Subject: Re: [PATCH 1/6] x86-mce: Modify CMCI poll interval to adjust for
 small check_interval values.

On Wed, Jul 09, 2014 at 02:24:31PM -0700, Havard Skinnemoen wrote:
> Date:	Wed, 9 Jul 2014 14:24:31 -0700
> From: Havard Skinnemoen <hskinnemoen@...gle.com>
> To: Borislav Petkov <bp@...en8.de>
> Cc: Tony Luck <tony.luck@...el.com>, Linux Kernel
>  <linux-kernel@...r.kernel.org>, Ewout van Bekkum <ewout@...gle.com>
> Subject: Re: [PATCH 1/6] x86-mce: Modify CMCI poll interval to adjust for
>  small check_interval values.
> 
> On Wed, Jul 9, 2014 at 12:17 PM, Borislav Petkov <bp@...en8.de> wrote:
> >
> > On Wed, Jul 09, 2014 at 10:09:21AM -0700, Havard Skinnemoen wrote:
> > > From: Ewout van Bekkum <ewout@...gle.com>
> > >
> > > The CMCI poll interval was updated to pick the minimum interval between
> > > the original 30 seconds and the check_interval divided by 8 (minimum of
> > > 3 polls).
> >
> > Why min 3 polls? How do you come up with exactly that frequency?
> 
> The idea is that if we make it equal to check_interval, it might
> bounce back and forth a lot. So we need to divide by something, and 8
> seems like a nice, safe value, and it seems to work well. We're not
> opposed to considering other values, of course (e.g. 2 and 4 might
> work well too, but with somewhat higher risk of ping-ponging).
That value looks chosen a little bit at will. How about updating
CMCI_POLL_INTERVAL when check_interval is changed to ensure
CMCI_POLL_INTERVAL <= check_interval always.

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