Re: [PATCH] mvsas: defer non-NCQ cmds when NCQ cmds are active

[David Milburn <dmilburn@redhat.com>]

James Bottomley wrote:
> On Tue, 2010-09-21 at 14:17 -0500, David Milburn wrote:
>> Non-NCQ commands should run exclusively, ata_qc_issue warns when mixing
>> non-NCQ and NCQ commands.
>>
>> Signed-off-by: David Milburn <dmilburn@redhat.com>
>> Reported-by: Konstantinos Skarlatos <k.skarlatos@gmail.com>
>> ---
>>  drivers/scsi/libsas/sas_ata.c |    1 +
>>  1 files changed, 1 insertions(+), 0 deletions(-)
>>
>> diff --git a/drivers/scsi/libsas/sas_ata.c b/drivers/scsi/libsas/sas_ata.c
>> index 042153c..ddbade7 100644
>> --- a/drivers/scsi/libsas/sas_ata.c
>> +++ b/drivers/scsi/libsas/sas_ata.c
>> @@ -347,6 +347,7 @@ static int sas_ata_scr_read(struct ata_link *link, unsigned int sc_reg_in,
>>  static struct ata_port_operations sas_sata_ops = {
>>  	.phy_reset		= sas_ata_phy_reset,
>>  	.post_internal_cmd	= sas_ata_post_internal,
>> +	.qc_defer               = ata_std_qc_defer,
> 
> What does this do on the card that doesn't need it: the aic94xx?  That
> one takes in a pipeline of commands and takes responsibility for getting
> the issue right.  Something like this throttles the pipeline higher than
> the aic94xx is expecting.  However, as long as it's not too much of a
> performance problem, I don't mind applying it.

James,

For any driver using sas_sata_ops, it could effect performance for
those drivers whose execute_task handles both, though I can't say
I am real familiar with aic94xx.

Thanks,
David



> 
> James
> 
>