Re: Patch added to scsi-rc-fixes-2.6: [SCSI] host lock push-down

Re: Patch added to scsi-rc-fixes-2.6: [SCSI] host lock push-down

[Jeff Garzik]

On 11/10/2010 05:40 PM, James Bottomley wrote:
> Your commit:
>
>      [SCSI] host lock push-down
>
>      Move the mid-layer's ->queuecommand() invocation from being locked
>      with the host lock to being unlocked to facilitate speeding up the
>      critical path for drivers who don't need this lock taken anyway.
>
>      The patch below presents a simple SCSI host lock push-down as an
>      equivalent transformation.  No locking or other behavior should change
>      with this patch.  All existing bugs and locking orders are preserved.
>
>      Minimal code disturbance was attempted with this change.  Most drivers
>      needed only two one-line modifications for their host lock push-down.
>
>      Signed-off-by: Jeff Garzik<jgarzik@redhat.com>
>      Signed-off-by: James Bottomley<James.Bottomley@suse.de>
>
> has been added to the upstream SCSI tree
> You can find it here:

No comments on renaming ->queuecommand to something else?

The consequences are rather dire if this goes unnoticed, yes?

	Jeff


In http://marc.info/?l=linux-ide&m=128891665713984&w=2 I wrote:
> An alternate arrangement, not presented by this patch, might
> be preferred:  in order to make it clear that queuecommand
> locking has changed, one could s/queuecommand/queuecommand_nl/ in
> Scsi_Host_Template, in order to guarantee that drivers are either
> (a) upgraded or (b) broken at compile time.  Compile-time detection of
> new locking may be desirable, and I'll volunteer to change my patch to
> do that, if community members prefer that route instead of below.

Re: Patch added to scsi-rc-fixes-2.6: [SCSI] host lock push-down

[James Bottomley]

On Wed, 2010-11-10 at 18:28 -0500, Jeff Garzik wrote:
> On 11/10/2010 05:40 PM, James Bottomley wrote:
> > Your commit:
> >
> >      [SCSI] host lock push-down
> >
> >      Move the mid-layer's ->queuecommand() invocation from being locked
> >      with the host lock to being unlocked to facilitate speeding up the
> >      critical path for drivers who don't need this lock taken anyway.
> >
> >      The patch below presents a simple SCSI host lock push-down as an
> >      equivalent transformation.  No locking or other behavior should change
> >      with this patch.  All existing bugs and locking orders are preserved.
> >
> >      Minimal code disturbance was attempted with this change.  Most drivers
> >      needed only two one-line modifications for their host lock push-down.
> >
> >      Signed-off-by: Jeff Garzik<jgarzik@redhat.com>
> >      Signed-off-by: James Bottomley<James.Bottomley@suse.de>
> >
> > has been added to the upstream SCSI tree
> > You can find it here:
> 
> No comments on renaming ->queuecommand to something else?

What we wondered about doing differently isn't really relevant for a
change log ... that should just really be about what was done (to avoid
confusion).

> The consequences are rather dire if this goes unnoticed, yes?

You mean if there's a missed in-tree driver?  Yes, but I took care to
make sure all SCSI drivers were accounted for.  For out of tree drivers,
as with the eh lock push down, it's caveat emptor.

James

Re: Patch added to scsi-rc-fixes-2.6: [SCSI] host lock push-down

[Jeff Garzik]

On 11/10/2010 06:45 PM, James Bottomley wrote:
> On Wed, 2010-11-10 at 18:28 -0500, Jeff Garzik wrote:
>> On 11/10/2010 05:40 PM, James Bottomley wrote:
>>> Your commit:
>>>
>>>       [SCSI] host lock push-down
>>>
>>>       Move the mid-layer's ->queuecommand() invocation from being locked
>>>       with the host lock to being unlocked to facilitate speeding up the
>>>       critical path for drivers who don't need this lock taken anyway.
>>>
>>>       The patch below presents a simple SCSI host lock push-down as an
>>>       equivalent transformation.  No locking or other behavior should change
>>>       with this patch.  All existing bugs and locking orders are preserved.
>>>
>>>       Minimal code disturbance was attempted with this change.  Most drivers
>>>       needed only two one-line modifications for their host lock push-down.
>>>
>>>       Signed-off-by: Jeff Garzik<jgarzik@redhat.com>
>>>       Signed-off-by: James Bottomley<James.Bottomley@suse.de>
>>>
>>> has been added to the upstream SCSI tree
>>> You can find it here:
>>
>> No comments on renaming ->queuecommand to something else?
>
> What we wondered about doing differently isn't really relevant for a
> change log ... that should just really be about what was done (to avoid
> confusion).

Wasn't referring to the changelog (perhaps shouldn't have quoted that); 
just asking the question generally.


>> The consequences are rather dire if this goes unnoticed, yes?
>
> You mean if there's a missed in-tree driver?  Yes, but I took care to
> make sure all SCSI drivers were accounted for.  For out of tree drivers,
> as with the eh lock push down, it's caveat emptor.

Thinking about out-of-tree drivers, yes.

	Jeff

Re: Patch added to scsi-rc-fixes-2.6: [SCSI] host lock push-down

[Nicholas A. Bellinger]

On Wed, 2010-11-10 at 18:52 -0500, Jeff Garzik wrote:
> On 11/10/2010 06:45 PM, James Bottomley wrote:
> > On Wed, 2010-11-10 at 18:28 -0500, Jeff Garzik wrote:
> >> On 11/10/2010 05:40 PM, James Bottomley wrote:
> >>> Your commit:
> >>>
> >>>       [SCSI] host lock push-down
> >>>
> >>>       Move the mid-layer's ->queuecommand() invocation from being locked
> >>>       with the host lock to being unlocked to facilitate speeding up the
> >>>       critical path for drivers who don't need this lock taken anyway.
> >>>
> >>>       The patch below presents a simple SCSI host lock push-down as an
> >>>       equivalent transformation.  No locking or other behavior should change
> >>>       with this patch.  All existing bugs and locking orders are preserved.
> >>>
> >>>       Minimal code disturbance was attempted with this change.  Most drivers
> >>>       needed only two one-line modifications for their host lock push-down.
> >>>
> >>>       Signed-off-by: Jeff Garzik<jgarzik@redhat.com>
> >>>       Signed-off-by: James Bottomley<James.Bottomley@suse.de>
> >>>
> >>> has been added to the upstream SCSI tree
> >>> You can find it here:
> >>
> >> No comments on renaming ->queuecommand to something else?
> >
> > What we wondered about doing differently isn't really relevant for a
> > change log ... that should just really be about what was done (to avoid
> > confusion).
> 
> Wasn't referring to the changelog (perhaps shouldn't have quoted that); 
> just asking the question generally.
> 
> 
> >> The consequences are rather dire if this goes unnoticed, yes?
> >
> > You mean if there's a missed in-tree driver?  Yes, but I took care to
> > make sure all SCSI drivers were accounted for.  For out of tree drivers,
> > as with the eh lock push down, it's caveat emptor.
> 
> Thinking about out-of-tree drivers, yes.
> 

Hi Jeff and James,

Thank you for getting this initial patch merged.  I really think this
was and is the best choice moving forward.   Also, a seriously big thank
you to all of the other folks who have helped identify LLDs issues for
host_lock less mode for drivers!!

In the next days I will get a atomic_t scsi_host->cmd_serial_number
patch rebased (which is really very minor at this point w/o the
scsi_error.c changes), and merge the current host_lock-less 'scoreboard'
on top of jgarzik's code and tag for .38.   So, please let me know if
you would to include minor the atomic_t scsi_host->cmd_serial_number
patch for .37 or if you would rather have this immediately preceed the
first series of "enable host-lock_less for LLD vendor superturbo hba"
for the .38 round.

Best,

--nab