From: Borislav Petkov <bp@alien8.de>
To: "Zheng, Lv" <lv.zheng@intel.com>
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: Tue, 28 Apr 2015 15:59:13 +0200 [thread overview]
Message-ID: <20150428135913.GD19025@pd.tnic> (raw)
In-Reply-To: <1AE640813FDE7649BE1B193DEA596E880270F835@SHSMSX101.ccr.corp.intel.com>
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.
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.
--
next prev parent reply other threads:[~2015-04-28 13:59 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 [this message]
2015-04-29 0:24 ` Zheng, Lv
2015-04-29 0:49 ` Zheng, Lv
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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