linux-kernel - Re: [PATCH 4/7] ide: ide_hwgroup_t.rq doesn't need an ide

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Date:	Fri, 10 Oct 2008 18:20:18 +0200
From:	Bartlomiej Zolnierkiewicz <bzolnier@...il.com>
To:	Elias Oltmanns <eo@...ensachen.de>
Cc:	linux-ide@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/7] ide: ide_hwgroup_t.rq doesn't need an ide_lock held

On Friday 10 October 2008, Elias Oltmanns wrote:
> Bartlomiej Zolnierkiewicz <bzolnier@...il.com> wrote:
> > From: Bartlomiej Zolnierkiewicz <bzolnier@...il.com>
> > Subject: [PATCH] ide: ide_hwgroup_t.rq doesn't need an ide_lock held
> >
> > While at it:
> > - no need to check for hwgroup presence in ide_dump_opcode()
> >
> > Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@...il.com>
> > ---
> [...]
> > Index: b/drivers/ide/ide-io.c
> > ===================================================================
> > --- a/drivers/ide/ide-io.c
> > +++ b/drivers/ide/ide-io.c
> [...]
> > @@ -274,7 +269,11 @@ static void ide_complete_pm_request (ide
> >  		drive->dev_flags &= ~IDE_DFLAG_BLOCKED;
> >  		blk_start_queue(drive->queue);
> >  	}
> > -	HWGROUP(drive)->rq = NULL;
> > +	spin_unlock_irqrestore(&ide_lock, flags);
> > +
> > +	drive->hwif->hwgroup->rq = NULL;
> > +
> > +	spin_lock_irqsave(&ide_lock, flags);
> >  	if (__blk_end_request(rq, 0, 0))
> >  		BUG();
> >  	spin_unlock_irqrestore(&ide_lock, flags);
> 
> Is it really an improvement to release the lock here?

Yes since it is a preparation for using the right lock here
(drive->queue->queue_lock instead of ide_lock) which is done
in patch #6/7:

@@ -263,10 +260,8 @@ static void ide_complete_pm_request (ide
 
 	drive->hwif->hwgroup->rq = NULL;
 
-	spin_lock_irqsave(&ide_lock, flags);
-	if (__blk_end_request(rq, 0, 0))
+	if (blk_end_request(rq, 0, 0))
 		BUG();
-	spin_unlock_irqrestore(&ide_lock, flags);
 }

[ ide_lock and drive->queue->queue_lock are the same lock at the moment
  (which is wrong since they are meant to protect completely different
  things) but after this patchset it should be quite easy to address  ]

Also ide_complete_pm_request() above is used only for completion of
PM suspend/resume requests and is not really performance critical.

Thanks,
Bart
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