From: NeilBrown <neilb@suse.de>
To: Shaohua Li <shli@kernel.org>
Cc: linux-raid@vger.kernel.org, axboe@kernel.dk,
dan.j.williams@intel.com, shli@fusionio.com
Subject: Re: [patch 1/8] raid5: add a per-stripe lock
Date: Thu, 7 Jun 2012 16:35:22 +1000 [thread overview]
Message-ID: <20120607163522.71c68e23@notabene.brown> (raw)
In-Reply-To: <20120607062939.GA779@kernel.org>
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On Thu, 7 Jun 2012 14:29:39 +0800 Shaohua Li <shli@kernel.org> wrote:
> On Thu, Jun 07, 2012 at 10:54:10AM +1000, NeilBrown wrote:
> > On Mon, 04 Jun 2012 16:01:53 +0800 Shaohua Li <shli@kernel.org> wrote:
> >
> > > Add a per-stripe lock to protect stripe specific data, like dev->read,
> > > written, ... The purpose is to reduce lock contention of conf->device_lock.
> >
> > I'm not convinced that you need to add a lock.
> > I am convinced that if you do add one you need to explain exactly what it is
> > protecting.
> >
> > The STRIPE_ACTIVE bit serves as a lock and ensures that only one process can
> > be in handle_stripe at a time.
> > So I don't think dev->read actually needs any protection (though I haven't
> > checked thoroughly).
> >
> > I think the only things that device_lock protects are things shared by
> > multiple stripes, so adding a per-stripe spinlock isn't going to help remove
> > device_lock.
>
> This sounds not true to me. both the async callbacks and request completion
> access stripe data, like dev->read. Such things are not protected by
> STRIPE_ACTIVE bit. Thought we can delete STRIPE_ACTIVE bit with stripe lock
> introduced.
Please give specifics. What race do you see with access to dev->read that is
not protected by STRIPE_ACTIVE ?
NeilBrown
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next prev parent reply other threads:[~2012-06-07 6:35 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-06-04 8:01 [patch 0/8] raid5: improve write performance for fast storage Shaohua Li
2012-06-04 8:01 ` [patch 1/8] raid5: add a per-stripe lock Shaohua Li
2012-06-07 0:54 ` NeilBrown
2012-06-07 6:29 ` Shaohua Li
2012-06-07 6:35 ` NeilBrown [this message]
2012-06-07 6:52 ` Shaohua Li
2012-06-12 21:02 ` Dan Williams
2012-06-13 4:08 ` Dan Williams
2012-06-13 4:23 ` Shaohua Li
2012-06-12 21:10 ` Dan Williams
2012-06-04 8:01 ` [patch 2/8] raid5: lockless access raid5 overrided bi_phys_segments Shaohua Li
2012-06-07 1:06 ` NeilBrown
2012-06-12 20:41 ` Dan Williams
2012-06-04 8:01 ` [patch 3/8] raid5: remove some device_lock locking places Shaohua Li
2012-06-04 8:01 ` [patch 4/8] raid5: reduce chance release_stripe() taking device_lock Shaohua Li
2012-06-07 0:50 ` NeilBrown
2012-06-04 8:01 ` [patch 5/8] raid5: add batch stripe release Shaohua Li
2012-06-04 8:01 ` [patch 6/8] raid5: make_request use " Shaohua Li
2012-06-07 1:23 ` NeilBrown
2012-06-07 6:33 ` Shaohua Li
2012-06-07 7:33 ` NeilBrown
2012-06-07 7:58 ` Shaohua Li
2012-06-08 6:16 ` Shaohua Li
2012-06-08 6:42 ` NeilBrown
2012-06-04 8:01 ` [patch 7/8] raid5: raid5d handle stripe in batch way Shaohua Li
2012-06-07 1:32 ` NeilBrown
2012-06-07 6:35 ` Shaohua Li
2012-06-07 7:38 ` NeilBrown
2012-06-04 8:02 ` [patch 8/8] raid5: create multiple threads to handle stripes Shaohua Li
2012-06-07 1:39 ` NeilBrown
2012-06-07 6:45 ` Shaohua Li
2012-06-13 4:08 ` Dan Williams
2012-06-21 10:09 ` Shaohua Li
2012-07-02 20:43 ` Dan Williams
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