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

From: Heng Qi <hengqi@linux.alibaba.com>
To: Jason Wang <jasowang@redhat.com>
Cc: netdev@vger.kernel.org, virtualization@lists.linux.dev,
	"Michael S. Tsirkin" <mst@redhat.com>,
	Jakub Kicinski <kuba@kernel.org>, Paolo Abeni <pabeni@redhat.com>,
	Eric Dumazet <edumazet@google.com>,
	"David S. Miller" <davem@davemloft.net>,
	Xuan Zhuo <xuanzhuo@linux.alibaba.com>
Subject: Re: [PATCH 2/2] virtio-net: reduce the CPU consumption of dim worker
Date: Mon, 25 Mar 2024 15:17:47 +0800	[thread overview]
Message-ID: <b54ad370-67bd-4b8c-82fb-54625e68288b@linux.alibaba.com> (raw)
In-Reply-To: <CACGkMEu8or7+fw3+vX_PY3Qsrm7zVSf6TS9SiE20NpOsz-or6g@mail.gmail.com>

在 2024/3/25 下午1:57, Jason Wang 写道:
> On Mon, Mar 25, 2024 at 10:21 AM Heng Qi <hengqi@linux.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@linux.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@linux.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.

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

YES.

Thanks,
Heng

>
> Thanks
>
>> Thanks,
>> Heng
>>
>>> Thanks