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: Tue, 28 Apr 2015 00:44:12 +0000 [thread overview]
Message-ID: <1AE640813FDE7649BE1B193DEA596E880270F55F@SHSMSX101.ccr.corp.intel.com> (raw)
In-Reply-To: <20150427084631.GA6774@pd.tnic>
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Hi,
> From: Borislav Petkov [mailto:bp@alien8.de]
> Sent: Monday, April 27, 2015 4:47 PM
>
> On Mon, Apr 27, 2015 at 03:16:00AM +0000, Zheng, Lv wrote:
> > > @@ -840,7 +840,9 @@ static int ghes_notify_nmi(unsigned int cmd, struct pt_regs *regs)
> > > struct ghes *ghes;
> > > int sev, ret = NMI_DONE;
> > >
> > > - raw_spin_lock(&ghes_nmi_lock);
> > > + if (!atomic_add_unless(&ghes_in_nmi, 1, 1))
> > > + return ret;
> > > +
> >
> > Just a simple question.
> > Why not just using cmpxchg here instead of atomic_add_unless so that no atomic_dec will be needed.
>
> What do you think atomic_add_unless ends up doing:
>
> #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.37056, MEM[(volatile u32 *)&ghes_in_nmi]
> # 0 "" 2
> #NO_APP
>
> And you need to atomic_dec() so that another reader can enter, i.e. how
> the exclusion primitive works.
>
> Or did you have something else in mind?
My mistake.
I mean cmpxchg() and xchg() (or atomic_cmpxchg() and atomic_xchg()) pair here, so nothing can be reduced.
But IMO, atomic_add_unless() is implemented via cmpxchg on many architectures.
And it might be better to use it directly here which is a bit faster as you actually only need one value switch here.
Thanks and best regards
-Lv
>
> --
> Regards/Gruss,
> Boris.
>
> ECO tip #101: Trim your mails when you reply.
> --
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next prev parent reply other threads:[~2015-04-28 0:44 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 [this message]
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
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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