Messages in this thread | | | From | Thomas Gleixner <> | Subject | Re: [PATCH RFC] blk-mq: Don't IPI requests on PREEMPT_RT | Date | Tue, 27 Oct 2020 18:05:15 +0100 |
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On Tue, Oct 27 2020 at 16:07, Christoph Hellwig wrote: > On Tue, Oct 27, 2020 at 11:11:02AM +0100, Sebastian Andrzej Siewior wrote: >> Right. I found this David Runge's log: > > True, ->bi_end_io instances can do a lot of things as long as they > are hardirq safe. > > And in the end the IPI case isn't the super fast path anyway, as it > means we don't use a queue per CPU. > > 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.
Thanks,
tglx
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