netdev - Re: [PATCH 2/2] virtio-net: reduce the CPU consumption of dim worker

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Message-ID: <CACGkMEvShZKd7AvMFtmEWBVGQsQrGkQMTEx8yQYYU0uYqp=uMg@mail.gmail.com>
Date: Mon, 25 Mar 2024 16:42:27 +0800
From: Jason Wang <jasowang@...hat.com>
To: Heng Qi <hengqi@...ux.alibaba.com>
Cc: netdev@...r.kernel.org, virtualization@...ts.linux.dev, 
	"Michael S. Tsirkin" <mst@...hat.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
	Eric Dumazet <edumazet@...gle.com>, "David S. Miller" <davem@...emloft.net>, 
	Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
Subject: Re: [PATCH 2/2] virtio-net: reduce the CPU consumption of dim worker

On Mon, Mar 25, 2024 at 4:22 PM Heng Qi <hengqi@...ux.alibaba.com> wrote:
>
>
>
> 在 2024/3/25 下午3:56, Jason Wang 写道:
> > On Mon, Mar 25, 2024 at 3:18 PM Heng Qi <hengqi@...ux.alibaba.com> wrote:
> >>
> >>
> >> 在 2024/3/25 下午1:57, Jason Wang 写道:
> >>> On Mon, Mar 25, 2024 at 10:21 AM Heng Qi <hengqi@...ux.alibaba.com> wrote:
> >>>>
> >>>> 在 2024/3/22 下午1:19, Jason Wang 写道:
> >>>>> On Thu, Mar 21, 2024 at 7:46 PM Heng Qi <hengqi@...ux.alibaba.com> wrote:
> >>>>>> Currently, ctrlq processes commands in a synchronous manner,
> >>>>>> which increases the delay of dim commands when configuring
> >>>>>> multi-queue VMs, which in turn causes the CPU utilization to
> >>>>>> increase and interferes with the performance of dim.
> >>>>>>
> >>>>>> Therefore we asynchronously process ctlq's dim commands.
> >>>>>>
> >>>>>> Signed-off-by: Heng Qi <hengqi@...ux.alibaba.com>
> >>>>> I may miss some previous discussions.
> >>>>>
> >>>>> But at least the changelog needs to explain why you don't use interrupt.
> >>>> Will add, but reply here first.
> >>>>
> >>>> When upgrading the driver's ctrlq to use interrupt, problems may occur
> >>>> with some existing devices.
> >>>> For example, when existing devices are replaced with new drivers, they
> >>>> may not work.
> >>>> Or, if the guest OS supported by the new device is replaced by an old
> >>>> downstream OS product, it will not be usable.
> >>>>
> >>>> Although, ctrlq has the same capabilities as IOq in the virtio spec,
> >>>> this does have historical baggage.
> >>> I don't think the upstream Linux drivers need to workaround buggy
> >>> devices. Or it is a good excuse to block configure interrupts.
> >> Of course I agree. Our DPU devices support ctrlq irq natively, as long
> >> as the guest os opens irq to ctrlq.
> >>
> >> If other products have no problem with this, I would prefer to use irq
> >> to solve this problem, which is the most essential solution.
> > Let's do that.
>
> Ok, will do.
>
> Do you have the link to the patch where you previously modified the
> control queue for interrupt notifications.
> I think a new patch could be made on top of it, but I can't seem to find it.

Something like this?

https://lore.kernel.org/lkml/6026e801-6fda-fee9-a69b-d06a80368621@redhat.com/t/

Note that

1) some patch has been merged
2) we probably need to drop the timeout logic as it's another topic
3) need to address other comments

THanks


>
> Thanks,
> Heng
>
> >
> > Thanks
> >
> >>> And I remember you told us your device doesn't have such an issue.
> >> YES.
> >>
> >> Thanks,
> >> Heng
> >>
> >>> Thanks
> >>>
> >>>> Thanks,
> >>>> Heng
> >>>>
> >>>>> Thanks
>