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From: "Zheng, Lv" <lv.zheng@intel.com>
To: Borislav Petkov <bp@alien8.de>
Cc: linux-edac <linux-edac@vger.kernel.org>,
	Jiri Kosina <jkosina@suse.cz>, Borislav Petkov <bp@suse.de>,
	"Rafael J. Wysocki" <rjw@rjwysocki.net>,
	"Len Brown" <lenb@kernel.org>, "Luck, Tony" <tony.luck@intel.com>,
	Tomasz Nowicki <tomasz.nowicki@linaro.org>,
	"Chen, Gong" <gong.chen@linux.intel.com>,
	Wolfram Sang <wsa@the-dreams.de>,
	Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>,
	"linux-acpi@vger.kernel.org" <linux-acpi@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: RE: [RFC PATCH 5/5] GHES: Make NMI handler have a single reader
Date: Wed, 29 Apr 2015 00:49:59 +0000	[thread overview]
Message-ID: <1AE640813FDE7649BE1B193DEA596E880270FB3B@SHSMSX101.ccr.corp.intel.com> (raw)
In-Reply-To: <20150428135913.GD19025@pd.tnic>

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Hi,

> From: Zheng, Lv
> Sent: Wednesday, April 29, 2015 8:25 AM
> Subject: RE: [RFC PATCH 5/5] GHES: Make NMI handler have a single reader
> 
> Hi,
> 
> > From: Borislav Petkov [mailto:bp@alien8.de]
> > Sent: Tuesday, April 28, 2015 9:59 PM
> > Subject: Re: [RFC PATCH 5/5] GHES: Make NMI handler have a single reader
> >
> > On Tue, Apr 28, 2015 at 01:38:41PM +0000, Zheng, Lv wrote:
> > > > -	raw_spin_lock(&ghes_nmi_lock);
> > > > +	if (!atomic_add_unless(&ghes_in_nmi, 1, 1))
> > > > +		return ret;
> > > > +
> > >
> > > if (atomic_cmpxchg(&ghes_in_nmi, 0, 1))
> > > 	return ret;
> >
> > Ok, now I understand what you mean.
> >
> > We absolutely want to use atomic_add_unless() because we get to save us
> > the expensive
> >
> > 	LOCK; CMPXCHG
> >
> > if the value was already 1. Which is exactly what this patch is trying
> > to avoid - a thundering herd of cores CMPXCHGing a global variable.
> 
> IMO, on most architectures, the "cmp" part should work just like what you've done with "if".
> And on some architectures, if the "xchg" doesn't happen, the "cmp" part even won't cause a pipe line hazard.

If you man the LOCK prefix, I understand now.

Thanks and best regards
-Lv

> 
> Thanks and best regards
> -Lv
> 
> 
> >
> > I.e.,
> >
> > 	movl	ghes_in_nmi(%rip), %ecx	# MEM[(const int *)&ghes_in_nmi], c
> > 	cmpl	$1, %ecx	#, c
> > 	je	.L311	#,				<--- exit here if ghes_in_nmi == 1.
> > 	leal	1(%rcx), %edx	#, D.37163
> > 	movl	%ecx, %eax	# c, c
> > #APP
> > # 177 "./arch/x86/include/asm/atomic.h" 1
> > 	.pushsection .smp_locks,"a"
> > .balign 4
> > .long 671f - .
> > .popsection
> > 671:
> > 	lock; cmpxchgl %edx,ghes_in_nmi(%rip)	# D.37163, MEM[(volatile u32 *)&ghes_in_nmi]
> > # 0 "" 2
> > #NO_APP
> >
> > --
> > Regards/Gruss,
> >     Boris.
> >
> > ECO tip #101: Trim your mails when you reply.
> > --
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  parent reply	other threads:[~2015-04-29  0:50 UTC|newest]

Thread overview: 32+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-03-27  9:22 [RFC PATCH 0/5] GHES NMI handler cleanup Borislav Petkov
2015-03-27  9:22 ` [RFC PATCH 1/5] GHES: Carve out error queueing in a separate function Borislav Petkov
2015-03-27  9:22 ` [RFC PATCH 2/5] GHES: Carve out the panic functionality Borislav Petkov
2015-03-27  9:22 ` [RFC PATCH 3/5] GHES: Panic right after detection Borislav Petkov
2015-03-27  9:22 ` [RFC PATCH 4/5] GHES: Elliminate double-loop in the NMI handler Borislav Petkov
2015-03-27  9:22 ` [RFC PATCH 5/5] GHES: Make NMI handler have a single reader Borislav Petkov
2015-04-01  7:45   ` Jiri Kosina
2015-04-01 13:49     ` Borislav Petkov
2015-04-23  8:39       ` Jiri Kosina
2015-04-23  8:59         ` Borislav Petkov
2015-04-23 18:00           ` Luck, Tony
2015-04-27 20:23             ` Borislav Petkov
2015-04-28 14:30     ` Don Zickus
2015-04-28 14:42       ` Don Zickus
2015-04-28 14:55       ` Borislav Petkov
2015-04-28 15:35         ` Don Zickus
2015-04-28 16:22           ` Borislav Petkov
2015-04-28 18:44             ` Don Zickus
2015-05-04 15:40               ` Borislav Petkov
2015-04-27  3:16   ` Zheng, Lv
2015-04-27  8:46     ` Borislav Petkov
2015-04-28  0:44       ` Zheng, Lv
2015-04-28  2:24       ` Zheng, Lv
2015-04-28  7:38         ` Borislav Petkov
2015-04-28 13:38   ` Zheng, Lv
2015-04-28 13:59     ` Borislav Petkov
2015-04-29  0:24       ` Zheng, Lv
2015-04-29  0:49       ` Zheng, Lv [this message]
2015-04-29  8:13         ` Borislav Petkov
2015-04-30  8:05           ` Zheng, Lv
2015-04-30  8:48             ` Borislav Petkov
2015-05-02  0:34               ` Zheng, Lv

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