[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <20150428135913.GD19025@pd.tnic>
Date: Tue, 28 Apr 2015 15:59:13 +0200
From: Borislav Petkov <bp@...en8.de>
To: "Zheng, Lv" <lv.zheng@...el.com>
Cc: linux-edac <linux-edac@...r.kernel.org>,
Jiri Kosina <jkosina@...e.cz>, Borislav Petkov <bp@...e.de>,
"Rafael J. Wysocki" <rjw@...ysocki.net>,
Len Brown <lenb@...nel.org>,
"Luck, Tony" <tony.luck@...el.com>,
Tomasz Nowicki <tomasz.nowicki@...aro.org>,
"Chen, Gong" <gong.chen@...ux.intel.com>,
Wolfram Sang <wsa@...-dreams.de>,
Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
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.
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.
--
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
Powered by blists - more mailing lists