Re: [PATCH] Don't retry SG_IO (REQ_BLOCK_PC) commands.

Patrick Mansfield
2003-11-20T21:51:33Z

On Thu, Nov 20, 2003 at 08:16:51PM +0100, Jens Axboe wrote:
> On Thu, Nov 20 2003, Mike Anderson wrote:
> > Patrick Mansfield [patmans@us.ibm.com] wrote:
> > > Don't retry SG_IO (REQ_BLOCK_PC) commands.
> >
> > Should we also have the REQ_BLOCK_PC requests set REQ_FAILFAST? The
> > patch to sd will imply the same behavior.
>
> Definitely!

Should the setting of REQ_FAILFAST be expanded to prevent requeueing after
a device or host reports queue full?

There are probably many SG_IO users that would want them retried, others
(multimedia?) might not want a retry. Multi-path would *not* want them
retried (well at least the host queue full).

For IO that cannot be sent to the device (if we have !scsi_dev_queue_ready()
or !scsi_host_queue_ready()), it is unclear if REQ_FAILFAST should
complete the IO without ever having sent it to the device.

If we expand the checks for REQ_FAILFAST, the SG_IO user interface should
allow the conditional setting of it.

-- Patrick Mansfield