Re: [PATCH] scsi_transport_fc: Make 'port_state' writeable

[Bart Van Assche <bvanassche@acm.org>]

On 03/15/13 19:51, Mike Christie wrote:
> On 03/15/2013 08:41 AM, Bart Van Assche wrote:
>> How about using the value of scsi_cmnd.jiffies_at_alloc to finish only
>> those SCSI commands in the host reset handler that exceeded a certain
>> processing time ?
>
> We basically do this now. When a scsi command times out the scsi layer
> blocks the host from processing new commands and waits for all
> outstanding commands to either finish normally or timeout. When all
> commands have finished or timedout, then we start the scsi eh code. So,
> by the time we have go to the scsi eh callbacks we are in a state where
> all the commands being processed by the eh have exceeded a certain
> processing time.
>
> If you mean you want to drop the block and wait part, then I think it
> could speed things up to do the abort callbacks while other IO is
> running (as long as the driver can support it). However if the abort
> fails and you need to escalate to operations like resets which interfere
> with multiple commands, then the driver/scsi-ml does not have much
> choice in what it does cleanup wise. There would be no point in checking
> the jiffies_at_alloc. The commands that are going to be affected by the
> tmf or host reset operation must be returned to the scsi-ml for retries
> or failure upwards.

Hello Mike,

It seems like there is a misunderstanding. With my comment I was not 
referring to the SCSI ML but to the SCSI LLD. LLD drivers like ib_srp 
keep track of outstanding SCSI requests. With the SRP protocol it is 
possible to tell the InfiniBand HCA not to deliver completions for 
outstanding requests by closing the connection used for SRP 
communication. Hence my suggestion to finish SCSI commands that were 
queued longer than a certain time ago from inside the LLD host reset 
handler. I'm not sure though whether all types of FC HBA's allow 
something equivalent.

Bart.