On 11/19/2010 06:02 AM, Desai, Kashyap wrote:
-----Original Message-----
From: Nicholas A. Bellinger [mailto:nab@xxxxxxxxxxxxxxx]
Sent: Friday, November 19, 2010 4:28 AM
To: Boaz Harrosh
Cc: linux-scsi; Jeff Garzik; James Bottomley; Christoph Hellwig; Mike
Christie; Vasu Dev; Tejun Heo; DL-MPT Fusion Linux; Desai, Kashyap
Subject: Re: [PATCH 06/11] mpt2sas: Convert to host_lock less w/
interrupts disabled externally
<Trimming CC list>
On Thu, 2010-11-18 at 12:15 +0200, Boaz Harrosh wrote:
On 11/18/2010 12:19 AM, Nicholas A. Bellinger wrote:
From: Nicholas Bellinger<nab@xxxxxxxxxxxxxxx>
This patch converts the mpt2sas driver to run in host_lock less
mode
with the new IRQ_DISABLE_SCSI_QCMD() that disables interrupts while
calling ->queuecommand() dispatch
Signed-off-by: Nicholas A. Bellinger<nab@xxxxxxxxxxxxxxx>
---
drivers/scsi/mpt2sas/mpt2sas_scsih.c | 6 +++---
1 files changed, 3 insertions(+), 3 deletions(-)
diff --git a/drivers/scsi/mpt2sas/mpt2sas_scsih.c
b/drivers/scsi/mpt2sas/mpt2sas_scsih.c
index 1a96a00..e564fe7 100644
--- a/drivers/scsi/mpt2sas/mpt2sas_scsih.c
+++ b/drivers/scsi/mpt2sas/mpt2sas_scsih.c
@@ -3304,7 +3304,7 @@ _scsih_eedp_error_handling(struct scsi_cmnd
*scmd, u16 ioc_status)
}
/**
- * _scsih_qcmd - main scsi request entry point
+ * _scsih_qcmd_irq_disable - main scsi request entry point
* @scmd: pointer to scsi command object
* @done: function pointer to be invoked on completion
*
@@ -3315,7 +3315,7 @@ _scsih_eedp_error_handling(struct scsi_cmnd
*scmd, u16 ioc_status)
* SCSI_MLQUEUE_HOST_BUSY if the entire host queue is full
*/
static int
-_scsih_qcmd_lck(struct scsi_cmnd *scmd, void (*done)(struct
scsi_cmnd *))
+_scsih_qcmd_irq_disable(struct scsi_cmnd *scmd, void
(*done)(struct scsi_cmnd *))
{
struct MPT2SAS_ADAPTER *ioc = shost_priv(scmd->device->host);
struct MPT2SAS_DEVICE *sas_device_priv_data;
@@ -3441,7 +3441,7 @@ _scsih_qcmd_lck(struct scsi_cmnd *scmd, void
(*done)(struct scsi_cmnd *))
return SCSI_MLQUEUE_HOST_BUSY;
}
-static DEF_SCSI_QCMD(_scsih_qcmd)
+static IRQ_DISABLE_SCSI_QCMD(_scsih_qcmd)
How can this (and other in the patchset) can be correct? I mean I
expect
that if you remove the lock,xx_qcmd_lck,unlock then inside the
xx_qcmd_lck
there was an unlock,do123,lock and that driver was effectively
running lockless
before. (like in iscsi). But here this is new behaviour. If it is
correct
I would like to see a statement from you that:
"I have audited this driver, and all shared resources are
protected by
XYZ so ..."
Otherwise how can I know this is correct? I have never audited this
driver myself
So for this specific mpt2sas case, Vasu Dev had been testing the
lock_less case w/o disabling interrupts for his original
SHT->unlocked_qcmd=1 patch, and from his comments this mode was stable
during his JBOD lock_less small block IOP performance test.
Nicholas, mpt2sas driver is safe even if in lock less condition.
I have tested mpt2sas driver available in 2.6.37-rc2 where I have seen host lock push down code is available for mpt2sas driver
I have seen static DEF_SCSI_QCMD(_scsih_qcmd) is available for mpt2sas driver. I also did testing removing that particular macro and making
Mpt2sas driver in actual host lock less mode. Below observation is after removing static DEF_SCSI_QCMD(_scsih_qcmd) from mpt2sas (that is what I refer as actual host lock less mode)
I have tested stability of the driver and I/O integrity. Things were fine. I am not seeing any need for even going for IRQ_DISABLE_SCSI_QCMD() patch too.
Mpt2sas driver is able to handle host lock less mode seamlessly, since we have all required (racy) places under spinlocks.
I do not see any solid need for this patch. Please correct me if I am missing anything here.
Which locks are held when setting or testing sas_target_priv_data->tm_busy?
ioc->ioc_link_reset_in_progress?
sas_target_priv_data->deleted?
Thanks,
Jeff
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