Re: [PATCH RFC] blk-mq: Don't IPI requests on PREEMPT_RT

[Sebastian Andrzej Siewior]

On 2020-10-27 17:23:09 [+0000], Christoph Hellwig wrote:
> On Tue, Oct 27, 2020 at 06:05:15PM +0100, Thomas Gleixner wrote:
> > > Is there a way to raise a softirq and preferably place it on a given
> > > CPU without our IPI dance?  That should be a win-win situation for
> > > everyone.
> > 
> > Not really. Softirq pending bits are strictly per cpu and we don't have
> > locking or atomics to set them remotely. Even if we had that, then you'd
> > still need a mechanism to make sure that the remote CPU actually
> > processes them. So you'd still need an IPI of some sorts.
> 
> Ok.  I was hoping we could hide this in core code somehow, especially
> a peterz didn't like the use of smp_call_function_single_async in the
> blk-mq completion code very much.
> 
> Sebastian, would this solve your preempt-rt and lockdep issues?

second. I'm cooking something.

Sebastian