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Message-Id: <1284692552.13344.143.camel@haakon2.linux-iscsi.org>
Date: Thu, 16 Sep 2010 20:02:32 -0700
From: "Nicholas A. Bellinger" <nab@...ux-iscsi.org>
To: James Bottomley <James.Bottomley@...e.de>
Cc: linux-scsi <linux-scsi@...r.kernel.org>,
linux-kernel <linux-kernel@...r.kernel.org>,
Vasu Dev <vasu.dev@...ux.intel.com>,
Tim Chen <tim.c.chen@...ux.intel.com>,
Andi Kleen <ak@...ux.intel.com>,
Matthew Wilcox <willy@...ux.intel.com>,
Mike Christie <michaelc@...wisc.edu>,
James Smart <james.smart@...lex.com>,
Andrew Vasquez <andrew.vasquez@...gic.com>,
FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>,
Hannes Reinecke <hare@...e.de>,
Joe Eykholt <jeykholt@...co.com>,
Christoph Hellwig <hch@....de>
Subject: Re: [PATCH 1/8] scsi: Drop struct Scsi_Host->host_lock around
SHT->queuecommand()
On Thu, 2010-09-16 at 22:46 -0400, James Bottomley wrote:
> On Thu, 2010-09-16 at 15:35 -0700, Nicholas A. Bellinger wrote:
> > From: Nicholas Bellinger <nab@...ux-iscsi.org>
> >
> > This patch converts scsi_dispatch_cmd() to only hold struct Scsi_Host->host_lock
> > for scsi_cmd_get_serial(), and drops the lock because the call into
> > the LLD with host->hostt->queuecommand().
> >
> > Signed-off-by: Nicholas A. Bellinger <nab@...ux-iscsi.org>
> > ---
> > drivers/scsi/scsi.c | 3 ++-
> > 1 files changed, 2 insertions(+), 1 deletions(-)
> >
> > diff --git a/drivers/scsi/scsi.c b/drivers/scsi/scsi.c
> > index ad0ed21..06e5b3a 100644
> > --- a/drivers/scsi/scsi.c
> > +++ b/drivers/scsi/scsi.c
> > @@ -745,6 +745,7 @@ int scsi_dispatch_cmd(struct scsi_cmnd *cmd)
> > * TODO: kill serial or move to blk layer
> > */
> > scsi_cmd_get_serial(host, cmd);
> > + spin_unlock_irqrestore(host->host_lock, flags);
>
> So at least from where I stand, my object is to reduce the number of
> times we take and release the lock, which this doesn't do. As I said
> before: we need to figure out the rest, which likely includes an atomic
> for the serial number (which is almost unused). I think the check
> against SHOST_DEL is fine unlocked.
>
Ok, this makes sense if the shost_state == SHOST_DEL check really is OK
to be done w/o host_lock held (I really don't know on this one..)
So if that is the case, then Tim and Vasu can you guys have a look at
dropping the host_lock around serial number usage and post this for
review..? I will plan to include the host_lock'less serial number patch
into lio-core-2.6.git/drop-host_lock with the rest of the LLD driver
conversion patches from this afternoon and respin a new branch for James
and Co. to review.
Thanks!
--nab
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