linux-kernel - Re: [PATCH 0/8] Drop host_lock around LLD SHT->queuecommand() caller

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Message-Id: <1284679082.13344.117.camel@haakon2.linux-iscsi.org>
Date:	Thu, 16 Sep 2010 16:18:02 -0700
From:	"Nicholas A. Bellinger" <nab@...ux-iscsi.org>
To:	linux-scsi <linux-scsi@...r.kernel.org>
Cc:	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>,
	James Bottomley <James.Bottomley@...e.de>,
	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>, Jeff Garzik <jeff@...zik.org>
Subject: Re: [PATCH 0/8] Drop host_lock around LLD SHT->queuecommand()
	caller

On Thu, 2010-09-16 at 16:01 -0700, Nicholas A. Bellinger wrote:
> On Thu, 2010-09-16 at 15:35 -0700, Nicholas A. Bellinger wrote:
> > From: Nicholas Bellinger <nab@...ux-iscsi.org>
> > 
> > Greetings all,
> > 
> > This series contains the first round of a whole-sale conversion for droping
> > struct Scsi_Host->host_lock around struct Scsi_Host->queuecommand() within
> > scsi_dispatch_cmd().  So with this first patch the only part of scsi_dispatch_cmd()
> > that is protected by host_lock is scsi_cmd_get_serial)_.
> > 
> > The patches #2 -> #8 converts libiscsi, libsas, lpfc, qla4xxx, qla2xxx,
> > TCM_Loop, and libfc code to drop their own SHT->queuecommand() internal
> > host_lock unlock() + lock() optimization that certain high performance libs
> > and LLDs have adopted over the years.  The changes involved here are really
> > quite straight forward, but please note that none of this code has been tested
> > with actual hardware yet, and is intended for generating comments for the relivent
> > SCSI LLD driver maintainers and other interested folks.
> > 
> > There are probably still be more LLDs which use this optimization, so please
> > let me know if there is another piece of SHT->queuecommand() caller code that
> > does this legacy optimization and needs to be updated.  I will be sure to
> > CC the right driver maintainers and CC linux-scsi as I come across any more
> > conversions.
> 
> Hi Guys,
> 
> drivers/scsi/fnic needs the conversion as well..  Here is that patch;
> 
> http://git.kernel.org/?p=linux/kernel/git/nab/lio-core-2.6.git;a=commitdiff;h=3c886b2ab6faccbe2803094deb7a9647199e5118
> 

Ok, after doing some more digging the BusLogic and the ever important
libata SCSI glue code use the legacy host_lock unlock() -> do_work ->
lock() optimization as well.  Here are those patches (jgarzik CC'ed):

buslogic: Remove host_lock unlock() + lock() from BusLogic_QueueCommand()
http://git.kernel.org/?p=linux/kernel/git/nab/lio-core-2.6.git;a=commitdiff;h=b465dfeb8e6950faa9c074681c72ca0a6c21276c

libata: Remove host_lock unlock() + lock() from ata_scsi_queuecmd()
http://git.kernel.org/?p=linux/kernel/git/nab/lio-core-2.6.git;a=commitdiff;h=29f2ded8876910d7eb84e4d270188de6f8a8c8ee

Thanks!

--nab

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