From: "Zheng, Lv" <lv.zheng@intel.com>
To: Borislav Petkov <bp@alien8.de>, linux-edac <linux-edac@vger.kernel.org>
Cc: 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 13:38:41 +0000 [thread overview]
Message-ID: <1AE640813FDE7649BE1B193DEA596E880270F835@SHSMSX101.ccr.corp.intel.com> (raw)
In-Reply-To: <1427448178-20689-6-git-send-email-bp@alien8.de>
Hi,
I was talking about this patch.
> From: Borislav Petkov [mailto:bp@alien8.de]
> Sent: Friday, March 27, 2015 5:23 PM
> Subject: [RFC PATCH 5/5] GHES: Make NMI handler have a single reader
>
> From: Jiri Kosina <jkosina@suse.cz>
>
> Since GHES sources are global, we theoretically need only a single CPU
> reading them per NMI instead of a thundering herd of CPUs waiting on a
> spinlock in NMI context for no reason at all.
>
> Do that.
>
> Signed-off-by: Jiri Kosina <jkosina@suse.cz>
> Signed-off-by: Borislav Petkov <bp@suse.de>
> ---
> drivers/acpi/apei/ghes.c | 12 +++++++-----
> 1 file changed, 7 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/acpi/apei/ghes.c b/drivers/acpi/apei/ghes.c
> index 94a44bad5576..2bfd53cbfe80 100644
> --- a/drivers/acpi/apei/ghes.c
> +++ b/drivers/acpi/apei/ghes.c
> @@ -729,10 +729,10 @@ static struct llist_head ghes_estatus_llist;
> static struct irq_work ghes_proc_irq_work;
>
> /*
> - * NMI may be triggered on any CPU, so ghes_nmi_lock is used for
> - * mutual exclusion.
> + * NMI may be triggered on any CPU, so ghes_in_nmi is used for
> + * having only one concurrent reader.
> */
> -static DEFINE_RAW_SPINLOCK(ghes_nmi_lock);
> +static atomic_t ghes_in_nmi = ATOMIC_INIT(0);
>
> static LIST_HEAD(ghes_nmi);
>
> @@ -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;
> +
if (atomic_cmpxchg(&ghes_in_nmi, 0, 1))
return ret;
> list_for_each_entry_rcu(ghes, &ghes_nmi, list) {
> if (ghes_read_estatus(ghes, 1)) {
> ghes_clear_estatus(ghes);
> @@ -863,7 +865,7 @@ static int ghes_notify_nmi(unsigned int cmd, struct pt_regs *regs)
> #ifdef CONFIG_ARCH_HAVE_NMI_SAFE_CMPXCHG
> irq_work_queue(&ghes_proc_irq_work);
> #endif
> - raw_spin_unlock(&ghes_nmi_lock);
> + atomic_dec(&ghes_in_nmi);
atomic_set(&ghes_in_nmi, 0);
It seems most of the drivers (under drivers/) are written in this way.
While the user of atomic_add_unless() is rare.
Can this work for you?
Thanks and best regards
-Lv
> return ret;
> }
>
> --
> 2.3.3
next prev parent reply other threads:[~2015-04-28 13:38 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 [this message]
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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