From: Matthew Wilcox <matthew@wil.cx>
To: "Moore, Eric" <Eric.Moore@lsi.com>
Cc: "Nandigama, Nagalakshmi" <Nagalakshmi.Nandigama@lsi.com>,
"stable@vger.kernel.org" <stable@vger.kernel.org>,
"linux-scsi@vger.kernel.org" <linux-scsi@vger.kernel.org>,
"Prakash, Sathya" <Sathya.Prakash@lsi.com>,
"jejb@kernel.org" <jejb@kernel.org>
Subject: Re: [PATCH] [SCSI] mpt2sas : Fix unsafe using smp_processor_id() in preemptible
Date: Tue, 17 Apr 2012 22:13:59 -0600 [thread overview]
Message-ID: <20120418041359.GB10862@parisc-linux.org> (raw)
In-Reply-To: <4565AEA676113A449269C2F3A549520FB5AE22E7@cosmail03.lsi.com>
On Tue, Apr 17, 2012 at 09:35:49PM -0600, Moore, Eric wrote:
> Jan Schmidt suggested using raw_smp_processor_id() back in February, see this: http://marc.info/?t=132974687100003&r=1&w=2
>
> Alex Shi recently suggested using preempt_disable() and preempt_enable() to solve the same issue, see this: http://marc.info/?t=133274303900003&r=1&w=2
>
> I believe the stack traces are there in both email discussion, they occur when CONFIG_DEBUG_PREEMPT is enabled.
>
> I would rather go with the solution giving the best performance. James Bottomley is there on the discussion with Jan Schmidt, he suggested using get_cpu() and put_cpu().
I use get_cpu() / put_cpu() in the NVMe driver in similar circumstances.
It's not noticable in the profiles :-)
Where my usage differs from the patch for mpt2sas is that I hold a
reference to the CPU over the submission. This works out well for
me because I have per-CPU state. Might be worth considering for your
driver ...
--
Matthew Wilcox Intel Open Source Technology Centre
"Bill, look, we understand that you're interested in selling us this
operating system, but compare it to ours. We can't possibly take such
a retrograde step."
next prev parent reply other threads:[~2012-04-18 4:14 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-04-17 5:55 [PATCH] [SCSI] mpt2sas : Fix unsafe using smp_processor_id() in preemptible nagalakshmi.nandigama
2012-04-18 3:14 ` Matthew Wilcox
2012-04-18 3:35 ` Moore, Eric
2012-04-18 4:13 ` Matthew Wilcox [this message]
2012-04-20 11:00 ` [PATCH] [SCSI] mpt2sas : Fix unsafe using smp_processor_id() inpreemptible Nandigama, Nagalakshmi
2012-04-23 1:29 ` Alex Shi
2012-04-20 11:07 ` [PATCH] [SCSI] mpt2sas : Fix unsafe using smp_processor_id() in preemptible James Bottomley
2012-04-27 10:39 ` Nandigama, Nagalakshmi
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