linux-kernel - [PATCH v2 00/11] Drop host_lock usage from scsi_dispatch

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Date:	Fri, 17 Sep 2010 11:21:37 -0700
From:	"Nicholas A. Bellinger" <nab@...ux-iscsi.org>
To:	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>,
	James Bottomley <James.Bottomley@...e.de>,
	Mike Christie <michaelc@...wisc.edu>
Cc:	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>,
	Nicholas Bellinger <nab@...ux-iscsi.org>
Subject: [PATCH v2 00/11] Drop host_lock usage from scsi_dispatch_cmd()

From: Nicholas Bellinger <nab@...ux-iscsi.org>

Greetings all,

This series contains the second round of a whole-sale conversion for completely
dropping struct Scsi_Host->host_lock usage within scsi_dispatch_cmd() for
the ML internal scsi_cmd_get_serial() and external SHT->queuecommand() LLD callers.

The main changes from comments from v1 -> v2 are:

	*) Make scsi_cmd_get_serial() use atomic_t and disable it's usage by default.
	*) Drop struct Scsi_Host->host_lock usage in scsi_dispatch_cmd()

For the v2 series, patch #1 converts struct Scsi_Host->cmd_serial_number to
atomic_t and adds struct Scsi_Host->use_serial_number to enabled usage.  This
patch also follows Joe Eykholt suggestion of using a +2 for each scsi_cmd_get_serial()
to ensure that the counter always wraps to a non-zero value.

Patch #2 completely removes host_lock usage from scsi_dispatch_cmd().

Patch #3 -> #6 remove the legacy host_lock lock() -> do_work() -> unlock()
optimization from generic libiscsi, libsas, libfc and libata ->queuecommand()
callers respectively.

And patches #7 -> #11 do the same conversion legacy host_lock lock() -> do_work() ->
unlock() for lpfc, qla4xxx, qla2xxx, fnic, and buslogic LLDs specific ->queuecommand()
callers.

There may 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 not in this list that need to be updated.  I will be sure to CC
the right driver maintainers and CC linux-scsi as I come across any more
conversions.

Many thanks to James Bottomley, Andi Keen, Joe Eykholt, Vasu Dev and
Tim Chen for their code and comments!

Signed-off-by: Nicholas A. Bellinger <nab@...ux-iscsi.org>

Nicholas Bellinger (11):
  scsi: Convert struct Scsi_Host->cmd_serial_number to atomic_t
  scsi: Drop struct Scsi_Host->host_lock usage in scsi_dispatch_cmd()
  libiscsi: Remove host_lock unlock() + lock() from
    iscsi_queuecommand()
  libsas: Remove host_lock unlock() + lock() from sas_queuecommand()
  libfc: Remove host_lock unlock() + lock() from fc_queuecommand()
  libata: Remove host_lock unlock() + lock() from ata_scsi_queuecmd()
  lpfc: Remove host_lock unlock() + lock() from lpfc_queuecommand()
  qla4xxx: Remove host_lock unlock() + lock() from
    qla4xxx_queuecommand()
  qla2xxx: Remove host_lock unlock() + lock() from
    qla2xxx_queuecommand()
  fnic: Remove host_lock unlock() + lock() from fnic_queuecommand()
  buslogic: Remove host_lock unlock() + lock() from
    BusLogic_QueueCommand()

 drivers/ata/libata-scsi.c           |    2 --
 drivers/scsi/BusLogic.c             |    4 ----
 drivers/scsi/fnic/fnic_scsi.c       |    9 ---------
 drivers/scsi/hosts.c                |    4 ++++
 drivers/scsi/libfc/fc_fcp.c         |    5 +----
 drivers/scsi/libiscsi.c             |    4 ----
 drivers/scsi/libsas/sas_scsi_host.c |    5 -----
 drivers/scsi/lpfc/lpfc_scsi.c       |    2 --
 drivers/scsi/qla2xxx/qla_os.c       |    7 ++-----
 drivers/scsi/qla4xxx/ql4_os.c       |    8 +-------
 drivers/scsi/scsi.c                 |   17 +++++++++++------
 include/scsi/scsi_host.h            |    8 +++++---
 12 files changed, 24 insertions(+), 51 deletions(-)

-- 
1.7.2.3

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