RE: [PATCH 0/3] megaraid_sas: Convert to host_lock less w/ interrupts disabled internally

["Nicholas A. Bellinger" <nab@linux-iscsi.org>]

On Tue, 2010-11-30 at 13:21 -0800, Nicholas A. Bellinger wrote:
> On Mon, 2010-11-29 at 23:26 -0700, Yang, Bo wrote:
> > Nicholas,
> >
> > Thanks for your patches (patches 1 -3).  We need to build the driver and provide it to our testing team to do
> > the full verification on lock_less kernel.
> 
> > The patch 2 and patch 3 changed the driver's major routines (I/O, get/return cmds routines and OCR routine).
> > I will keep update after we did the internal patch re-view for those changes as well as the testing team
> > give us the report.
> > 
> 
> Great, thanks for moving forward on the lock_less conversion..  Please
> let me know if you have any other questions.
> 
> > By the way, can you send me the full link of: lio-core-2.6.git/lock_less-LLDs-for-38-v2?  I am try to understand the changes for patch 3
> 
> 
> The patch #3 in full context is available here:
> 
> http://git.kernel.org/?p=linux/kernel/git/nab/lio-core-2.6.git;a=blob;f=drivers/scsi/megaraid/megaraid_sas.c;h=c42e1e4ef8c9923d9a930fa631f8d65455afadd6;hb=lock_less-LLDs-for-38-v2
> 
> Thanks!
> 
> --nab
> 
> 

Hi Bo,

I also noticed that __megasas_get_cmd() still needs the initial *cmd =
NULL assignment.  Pushing the following into lock_less-LLDs-for-38-v2
now:

Subject: [PATCH] megaraid_sas: Add NULL assignment in __megasas_get_cmd()

This patch changes the initial struct megasas_cmd *cmd to NULL,
which follows the pre lock_less conversion code.

Signed-off-by: Nicholas A. Bellinger <nab@linux-iscsi.org>
---
 drivers/scsi/megaraid/megaraid_sas.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/drivers/scsi/megaraid/megaraid_sas.c b/drivers/scsi/megaraid/megaraid_sas.c
index c42e1e4..be956a5 100644
--- a/drivers/scsi/megaraid/megaraid_sas.c
+++ b/drivers/scsi/megaraid/megaraid_sas.c
@@ -131,7 +131,7 @@ megasas_complete_cmd(struct megasas_instance *instance, struct megasas_cmd *cmd,
 static struct megasas_cmd *
 __megasas_get_cmd(struct megasas_instance *instance)
 {
-       struct megasas_cmd *cmd;
+       struct megasas_cmd *cmd = NULL;

        if (!list_empty(&instance->cmd_pool)) {
                cmd = list_entry((&instance->cmd_pool)->next,
-- 
1.7.2.3

Thanks!

--nab

> > +	struct megasas_cmd *cmd;
> >  	unsigned long flags;
> > -	struct megasas_cmd *cmd = NULL;
> > 
> > And 
> > 
> > +megasas_get_cmd(struct megasas_instance *instance) {
> > +	struct megasas_cmd *cmd;
> > +	unsigned long flags;
> > +
> > +	spin_lock_irqsave(&instance->cmd_pool_lock, flags);
> > +	cmd = __megasas_get_cmd(instance);
> >  	spin_unlock_irqrestore(&instance->cmd_pool_lock, flags);
> > +
> >  	return cmd;
> >  }     
> > 
> > Regards,
> > 
> > Bo Yang  
> > 
> > -----Original Message-----
> > From: linux-scsi-owner@vger.kernel.org [mailto:linux-scsi-owner@vger.kernel.org] On Behalf Of Nicholas A. Bellinger
> > Sent: Sunday, November 28, 2010 2:18 AM
> > To: linux-scsi; Hannes Reinecke; Yang, Bo
> > Cc: Christoph Hellwig; James Bottomley; Nicholas Bellinger
> > Subject: [PATCH 0/3] megaraid_sas: Convert to host_lock less w/ interrupts disabled internally
> > 
> > From: Nicholas Bellinger <nab@linux-iscsi.org>
> > 
> > Greetings Hannes, Bo and Co,
> > 
> > This series converts megaraid_sas to run in modern host_lock-less mode
> > for >= .37-rc3+ with interrupts disabled internally around megasas_instance->hba_lock.
> > This series is currently living in lio-core-2.6.git/lock_less-LLDs-for-38-v2,
> > and is intended for .38 mainline code.
> > 
> > The first patch adds a handful of missing barriers around instance->fw_outstanding
> > usage w/ atomic_add() and atomic_dec().
> > 
> > The second converts instance->issuepend_done to an atomic_t, along with
> > the necessary assignments in order to run w/ Scsi_Host->host_lock, and
> > without instance->hba_lock.
> > 
> > The third patch does the actual conversion, and adds a __megasas_get_cmd()
> > usased by megasas_queue_command() w/ instance->hba_lock, along with
> > being held for megasas_build_ldio() and megasas_build_dcdb() in order
> > to locate the proper frame for struct megasas_cmd.  This is really the
> > one major change in order to get host_lock-less to function with interrupts
> > disabled around hba_lock.
> > 
> > So far this has been tested with Hannes's QEMU 8708EM2 HBA emulation with
> > TCM_Loop backends using SG_IO from KVM host in a paired Host/Guest .37-rc3
> > environment.  This has not been tested on real silicon yet, but I believe
> > this series should be working there as well.
> > 
> > Comments are welcome, thanks!
> > 
> > Signed-off-by: Nicholas A. Bellinger <nab@linux-iscsi.org>
> > 
> > Nicholas Bellinger (3):
> >   megaraid_sas: Add smp_mb__after_atomic_*() for
> >     instance->fw_outstanding
> >   megaraid_sas: Convert instance->issuepend_done to atomic_t
> >   megaraid_sas: Convert SHT->queuecommand() to run host_lock-less
> > 
> >  drivers/scsi/megaraid/megaraid_sas.c |   84 ++++++++++++++++++++++-----------
> >  drivers/scsi/megaraid/megaraid_sas.h |    2 +-
> >  2 files changed, 57 insertions(+), 29 deletions(-)
> > 
> 
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