From: Jason Wang <jasowang@redhat.com>
To: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Halil Pasic <pasic@linux.ibm.com>,
Cornelia Huck <cohuck@redhat.com>,
linux-kernel <linux-kernel@vger.kernel.org>,
virtualization <virtualization@lists.linux-foundation.org>,
Stefano Garzarella <sgarzare@redhat.com>,
eperezma <eperezma@redhat.com>, Cindy Lu <lulu@redhat.com>,
Thomas Gleixner <tglx@linutronix.de>,
Peter Zijlstra <peterz@infradead.org>,
"Paul E. McKenney" <paulmck@kernel.org>,
Marc Zyngier <maz@kernel.org>
Subject: Re: [PATCH V3 6/9] virtio-ccw: implement synchronize_cbs()
Date: Tue, 26 Apr 2022 12:07:39 +0800 [thread overview]
Message-ID: <CACGkMEve+3ugK-Kgao3_2wbjb=fbF7AO2uEuArGjKgEAQcGdiQ@mail.gmail.com> (raw)
In-Reply-To: <20220425235415-mutt-send-email-mst@kernel.org>
On Tue, Apr 26, 2022 at 11:55 AM Michael S. Tsirkin <mst@redhat.com> wrote:
>
> On Mon, Apr 25, 2022 at 11:53:24PM -0400, Michael S. Tsirkin wrote:
> > On Tue, Apr 26, 2022 at 11:42:45AM +0800, Jason Wang wrote:
> > >
> > > 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
> > >
> >
> > rwlock is still a shared cacheline bouncing between CPUs and
> > a bunch of ordering instructions.
Yes, but it should be faster than spinlocks anyhow.
> > Maybe something per-cpu + some IPIs to run things on all CPUs instead?
Is this something like a customized version of synchronzie_rcu_expedited()?
>
> ... and I think classic and device interrupts are different enough
> here ...
Yes.
Thanks
>
> > > >
> > > > > --
> > > > > MST
>
next prev parent reply other threads:[~2022-04-26 4:08 UTC|newest]
Thread overview: 52+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-04-25 2:44 [PATCH V3 0/9] rework on the IRQ hardening of virtio Jason Wang
2022-04-25 2:44 ` [PATCH V3 1/9] virtio: use virtio_device_ready() in virtio_device_restore() Jason Wang
2022-04-28 9:07 ` Cornelia Huck
2022-04-25 2:44 ` [PATCH V3 2/9] virtio: use virtio_reset_device() when possible Jason Wang
2022-04-28 9:07 ` Cornelia Huck
2022-04-25 2:44 ` [PATCH V3 3/9] virtio: introduce config op to synchronize vring callbacks Jason Wang
2022-04-28 9:13 ` Cornelia Huck
2022-04-29 2:08 ` Jason Wang
2022-04-29 7:25 ` Cornelia Huck
2022-05-05 8:15 ` Jason Wang
2022-04-25 2:44 ` [PATCH V3 4/9] virtio-pci: implement synchronize_cbs() Jason Wang
2022-04-25 2:44 ` [PATCH V3 5/9] virtio-mmio: " Jason Wang
2022-04-25 2:44 ` [PATCH V3 6/9] virtio-ccw: " Jason Wang
2022-04-25 8:08 ` Michael S. Tsirkin
2022-04-25 8:54 ` Cornelia Huck
2022-04-25 13:59 ` Michael S. Tsirkin
2022-04-26 2:29 ` Halil Pasic
2022-04-26 3:35 ` Michael S. Tsirkin
2022-04-26 3:38 ` Michael S. Tsirkin
2022-04-26 3:42 ` Jason Wang
2022-04-26 3:53 ` Michael S. Tsirkin
2022-04-26 3:55 ` Michael S. Tsirkin
2022-04-26 4:07 ` Jason Wang [this message]
2022-04-26 6:30 ` Michael S. Tsirkin
2022-04-27 3:53 ` Jason Wang
2022-04-27 6:28 ` Michael S. Tsirkin
2022-04-27 6:30 ` Michael S. Tsirkin
2022-04-27 7:57 ` Jason Wang
2022-04-27 15:15 ` Michael S. Tsirkin
2022-04-26 15:47 ` Cornelia Huck
2022-04-26 16:43 ` Michael S. Tsirkin
2022-04-27 9:27 ` Cornelia Huck
2022-04-28 2:43 ` Halil Pasic
2022-04-28 3:04 ` Jason Wang
2022-04-28 5:24 ` Michael S. Tsirkin
2022-04-28 5:51 ` Jason Wang
2022-04-28 5:55 ` Michael S. Tsirkin
2022-04-28 6:02 ` Jason Wang
2022-04-28 6:17 ` Michael S. Tsirkin
2022-04-28 7:42 ` Cornelia Huck
2022-04-29 2:02 ` Jason Wang
2022-04-28 4:12 ` Michael S. Tsirkin
2022-04-26 2:50 ` Halil Pasic
2022-04-26 3:46 ` Jason Wang
[not found] ` <20220426053856.3325-1-hdanton@sina.com>
2022-04-26 5:59 ` Jason Wang
2022-04-25 2:44 ` [PATCH V3 7/9] virtio: allow to unbreak virtqueue Jason Wang
2022-04-25 12:44 ` Cornelia Huck
2022-04-25 14:04 ` Michael S. Tsirkin
2022-04-26 3:45 ` Jason Wang
2022-04-25 2:44 ` [PATCH V3 8/9] virtio: harden vring IRQ Jason Wang
2022-04-25 2:44 ` [PATCH V3 9/9] virtio: use WARN_ON() to warning illegal status value Jason Wang
2022-04-25 2:49 ` [PATCH V3 0/9] rework on the IRQ hardening of virtio Jason Wang
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