Messages in this thread | | | Date | Tue, 26 Apr 2022 11:42:45 +0800 | Subject | Re: [PATCH V3 6/9] virtio-ccw: implement synchronize_cbs() | From | Jason Wang <> |
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在 2022/4/26 11:38, Michael S. Tsirkin 写道: > On Mon, Apr 25, 2022 at 11:35:41PM -0400, Michael S. Tsirkin wrote: >> On Tue, Apr 26, 2022 at 04:29:11AM +0200, Halil Pasic wrote: >>> On Mon, 25 Apr 2022 09:59:55 -0400 >>> "Michael S. Tsirkin" <mst@redhat.com> wrote: >>> >>>> On Mon, Apr 25, 2022 at 10:54:24AM +0200, Cornelia Huck wrote: >>>>> On Mon, Apr 25 2022, "Michael S. Tsirkin" <mst@redhat.com> wrote: >>>>> >>>>>> On Mon, Apr 25, 2022 at 10:44:15AM +0800, Jason Wang wrote: >>>>>>> This patch tries to implement the synchronize_cbs() for ccw. For the >>>>>>> vring_interrupt() that is called via virtio_airq_handler(), the >>>>>>> synchronization is simply done via the airq_info's lock. For the >>>>>>> vring_interrupt() that is called via virtio_ccw_int_handler(), a per >>>>>>> device spinlock for irq is introduced ans used in the synchronization >>>>>>> method. >>>>>>> >>>>>>> Cc: Thomas Gleixner <tglx@linutronix.de> >>>>>>> Cc: Peter Zijlstra <peterz@infradead.org> >>>>>>> Cc: "Paul E. McKenney" <paulmck@kernel.org> >>>>>>> Cc: Marc Zyngier <maz@kernel.org> >>>>>>> Cc: Halil Pasic <pasic@linux.ibm.com> >>>>>>> Cc: Cornelia Huck <cohuck@redhat.com> >>>>>>> Signed-off-by: Jason Wang <jasowang@redhat.com> >>>>>> >>>>>> This is the only one that is giving me pause. Halil, Cornelia, >>>>>> should we be concerned about the performance impact here? >>>>>> Any chance it can be tested? >>>>> We can have a bunch of devices using the same airq structure, and the >>>>> sync cb creates a choke point, same as registering/unregistering. >>>> BTW can callbacks for multiple VQs run on multiple CPUs at the moment? >>> I'm not sure I understand the question. >>> >>> I do think we can have multiple CPUs that are executing some portion of >>> virtio_ccw_int_handler(). So I guess the answer is yes. Connie what do you think? >>> >>> On the other hand we could also end up serializing synchronize_cbs() >>> calls for different devices if they happen to use the same airq_info. But >>> this probably was not your question >> >> I am less concerned about synchronize_cbs being slow and more about >> the slowdown in interrupt processing itself. >> >>>> this patch serializes them on a spinlock. >>>> >>> Those could then pile up on the newly introduced spinlock. >>> >>> Regards, >>> Halil >> Hmm yea ... not good. > Is there any other way to synchronize with all callbacks?
Maybe using rwlock as airq handler?
Thanks
> >> -- >> MST
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