Re: [PATCH] scsi_execute_async() should add to the tail of the queue

[Dan Aloni]

Arjan van de Ven wrote:
> On Tue, 2006-12-19 at 10:35 +0200, Dan Aloni wrote:
>   
> > Hello,
> >
> > scsi_execute_async() has replaced scsi_do_req() a few versions ago, 
> > but it also incurred a change of behavior. I noticed that over-queuing 
> > a SCSI device using that function causes I/Os to be starved from 
> > low-level queuing for no justified reason.
> >  
> > I think it makes much more sense to perserve the original behaviour 
> > of scsi_do_req() and add the request to the tail of the queue.
> >     
>
> Hi,
>
> some things should really be added to the head of the queue, like
> maintenance requests and error handling requests. Are you sure this is
> the right change? At least I'd expect 2 apis, one for a head and one for
> a "normal" queueing...
>   
Since a user of scsi_execute_async() would most likely want to have
control over this, it would be better to add a parameter and fix the
current users of the function.

However, if we take this route we might have duplicate code
across mid-layer drivers (sg, st, osst), because they may choose to
prioritize I/Os in similar ways.

So instead of adding a parameter, we can make scsi_execute_async()
decide for itself based on the SCSI command, with read/write I/Os
taking the lowest priority.

Suggestions?

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