Re: [PATCH] blk-mq: use __smp_call_function_single directly

[Jens Axboe <axboe@kernel.dk>]

On Thu, Jan 09 2014, Christoph Hellwig wrote:
> On Wed, Jan 08, 2014 at 02:31:15PM -0700, Jens Axboe wrote:
> > On 01/08/2014 10:33 AM, Christoph Hellwig wrote:
> > > __smp_call_function_single already avoids multiple IPIs by internally
> > > queing up the items, and now also is available for non-SMP builds as
> > > a trivially correct stub, so there is no need to wrap it.  If the
> > > additional lock roundtrip cause problems my patch to convert the
> > > generic IPI code to llists is waiting to get merged will fix it.
> > 
> > Thanks Christoph, applied it.
> 
> Btw, the same should be done to the null_blk ipi completion
> path in theory.  But given that it always tries to IPI the local
> CPU __smp_call_function_single turns into a simple indirect function
> call, so I don't really understand the point of that code path at all.

The idea would be to have it forced be remote, on the given CPU, not
always just go local. So it just needs to be fixed up, it doesn't make
a lot of sense as it stands as a separate completion method.

-- 
Jens Axboe