Re: [RFC PATCH 5/5] GHES: Make NMI handler have a single reader

From: Borislav Petkov <bp@alien8.de>
To: Don Zickus <dzickus@redhat.com>
Cc: Jiri Kosina <jkosina@suse.cz>,
	linux-edac <linux-edac@vger.kernel.org>,
	Borislav Petkov <bp@suse.de>,
	"Rafael J. Wysocki" <rjw@rjwysocki.net>,
	Len Brown <lenb@kernel.org>, Tony Luck <tony.luck@intel.com>,
	Tomasz Nowicki <tomasz.nowicki@linaro.org>,
	"Chen, Gong" <gong.chen@linux.intel.com>,
	Wolfram Sang <wsa@the-dreams.de>, Lv Zheng <lv.zheng@intel.com>,
	Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>,
	linux-acpi@vger.kernel.org, linux-kernel@vger.kernel.org,
	Huang Ying <ying.huang@intel.com>
Subject: Re: [RFC PATCH 5/5] GHES: Make NMI handler have a single reader
Date: Tue, 28 Apr 2015 18:22:29 +0200	[thread overview]
Message-ID: <20150428162229.GH19025@pd.tnic> (raw)
In-Reply-To: <20150428153521.GE98296@redhat.com>

On Tue, Apr 28, 2015 at 11:35:21AM -0400, Don Zickus wrote:
> Your solution seems much simpler. :-)

... and I love simpler :-)

> I followed up in another email stating I mis-spoke.  I forgot this still
> uses the NMI_LOCAL shared NMI.  So every perf NMI, will also call the GHES
> handler to make sure NMIs did not piggy back each other.  So I don't believe

And this is something we should really fix - perf and RAS should
not have anything to do with each other. But I don't know the NMI
code to even have an idea how. I don't even know whether we can
differentiate NMIs, hell, I can't imagine the hardware giving us a
different NMI reason through get_nmi_reason(). Maybe that byte returned
from NMI_REASON_PORT is too small and hangs on too much legacy crap to
even be usable. Questions over questions...

> the NMI reason lock is called a majority of the time (except when the NMI is
> swallowed, but that is under heavy perf load...).

..

> We both agree the mechanics of the spinlock are overkill here and cause much
> cache contention.  Simplifying it to just 'reads' and return removes most of
> the problem.

Right.

-- 
Regards/Gruss,
    Boris.

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