I am just thinking how to make commands interval time shorter to have better
performance.
Meanwhile, there is an NCQ feature in SATA specification and block layer also
support tagging, but why we can not utilize this functionality because always
only one command is sent out per time and the tag number is zero even enable
NCQ.
Regards,
BingJiun
On Fri, Jan 14, 2011 at 1:47 PM, Robert Hancock <hancockrwd@xxxxxxxxx> wrote:
> On 01/13/2011 07:06 PM, 羅秉鈞 wrote:
>>
>> Hi,
>>
>> Yes, what I see is every time scsi_request_fn is called, we can only pop
>> up one request to be dispatched. So, How can we make block layer to
>> pass more than one commands to us? So that we can fill up more
>> commands into the Command List before write Px.CI. I think it might
>> shorten the command interval time.
>>
>> Even I enable the NCQ, I observed that there is only one command to be
>> executed per time and tag 0 is used.
>
> That sounds like the I/O pattern doesn't result in any concurrent transfers
> being executed. What kind of workload is this running?
>
>>
>> Is there any possible to change the libata and ahci.c to be able to fire
>> up
>> more than one commands at one time and report complete multiple to
>> upper layer(SCSI and block layer).
>>
>> Another question, at scsi_adjust_queue_depth() function, why
>> sdev->ordered_tags
>> and sdev->simple_tags value is only 0 or 1 regardless of queue_depth? What
>> does it mean?
>>
>> Thank you in advance for your explanation.
>>
>>
>>
>> On Fri, Jan 14, 2011 at 1:46 AM, Jeff Garzik<jeff@xxxxxxxxxx> wrote:
>>>
>>> On 01/13/2011 05:52 AM, 羅秉鈞 wrote:
>>>>
>>>> Hello,
>>>>
>>>> Inside ahci_qc_issue() function, I see that driver always write one bit
>>>> to Px.CI register even enable the NCQ.
>>>>
>>>> AHCI allows to fire 32 commands at one time and AHCI driver also
>>>> claims itself able to queue up to 31 commands.
>>>>
>>>> Inside ahci.c :
>>>> static struct scsi_host_template ahci_sht = {
>>>> ATA_NCQ_SHT(DRV_NAME),
>>>> .can_queue = AHCI_MAX_CMDS - 1,
>>>> ............
>>>>
>>>> Why upper layer(Block or SCSI layer) does not fill up as many as
>>>> possible
>>>> commands into Command List before sending the commands out
>>>> (Write to Px.CI register)?
>>>
>>> The driver successfully executes up to 31 commands at a time, in paralle.
>>>
>>> We submit one command at a time to hardware because the block layer
>>> passes
>>> commands to us one at a time.
>>>
>>> Jeff
>>>
>>>
>>>
>>>
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