Re: PATCH 5/5: scsi-scan-inq-timeout

[Kurt Garloff <garloff@suse.de>]

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Hi Patrick,

On Wed, Apr 21, 2004 at 01:24:54PM -0700, Patrick Mansfield wrote:
> SCSI_TIMEOUT is 2 * HZ.
> 
> So we defaulted to 6 seconds, and now we default to 5.5 seconds. Why?

True.

I have added half a second to be safe against 0.
Thus, I had the choice of rounding 6 to 6.5 or 5.5.
I chose 5.5, because the old value was chosen very conservative, as it
had to be enough for even sick devices. Now we have a boot parameter
to accomodate these, thus we can be less conservative. Thus 5.5.

> Why not get rid of the HZ/2, and set scsi_inq_timeout = SCSI_TIMEOUT/HZ +
> 4 so we default to 6 again?
> 
> So if a device needs at least N + .5 seconds then just set the
> scsi_inq_timeout to N + 1.

Why do you dislike HZ/2. The number is computed by the compiler at
compile time ...

> >  	SCSI_LOG_SCAN_BUS(3, printk(KERN_INFO "scsi scan: 1st INQUIRY %s with"
> >  			" code 0x%x\n", sreq->sr_result ?
> > @@ -393,7 +400,7 @@ static void scsi_probe_lun(struct scsi_r
> >  		memset(inq_result, 0, possible_inq_resp_len);
> >  		scsi_wait_req(sreq, (void *) scsi_cmd,
> >  			      (void *) inq_result,
> > -			      possible_inq_resp_len, SCSI_TIMEOUT + 4 * HZ, 3);
> > +			      possible_inq_resp_len, (1+scsi_inq_timeout)*(HZ/2), 3);
> 
> IMO just make the two timeouts the same and avoid any potential problems
> (like some funky device always takes 4 seconds to reponsd to an INQUIRY).

It's really only the reset recivery time which makes us choose such long
times. Otherwise SCSI_TIMEOUT would be _plenty_ of time to answer an 
INQUIRY. An INQUIRY is easier: No medium access is needed, see SPC3.
When this second INQUIRY is done, a first one has succeeded already, so 
the recovery from the reset has happened already.

Anyway, if you dislike it, I don't care much. If the first INQUIRY
succeeded, it's very unlikely that the second one fails, so the timeout
is even less important in real life.

Regards,
-- 
Kurt Garloff  <garloff@suse.de>                            Cologne, DE 
SUSE LINUX AG, Nuernberg, DE                          SUSE Labs (Head)

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