netdev - Re: [PATCH RFC 1/2] virtio-net: bql support

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Message-ID: <01e0fe8f-bd75-c39b-9d77-c5a9baf87348@redhat.com>
Date:   Wed, 2 Jan 2019 11:30:11 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     linux-kernel@...r.kernel.org, maxime.coquelin@...hat.com,
        tiwei.bie@...el.com, wexu@...hat.com, jfreimann@...hat.com,
        "David S. Miller" <davem@...emloft.net>,
        virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org
Subject: Re: [PATCH RFC 1/2] virtio-net: bql support


On 2018/12/31 上午2:48, Michael S. Tsirkin wrote:
> On Thu, Dec 27, 2018 at 06:04:53PM +0800, Jason Wang wrote:
>> On 2018/12/26 下午11:22, Michael S. Tsirkin wrote:
>>> On Thu, Dec 06, 2018 at 04:17:36PM +0800, Jason Wang wrote:
>>>> On 2018/12/6 上午6:54, Michael S. Tsirkin wrote:
>>>>> When use_napi is set, let's enable BQLs.  Note: some of the issues are
>>>>> similar to wifi.  It's worth considering whether something similar to
>>>>> commit 36148c2bbfbe ("mac80211: Adjust TSQ pacing shift") might be
>>>>> benefitial.
>>>> I've played a similar patch several days before. The tricky part is the mode
>>>> switching between napi and no napi. We should make sure when the packet is
>>>> sent and trakced by BQL,  it should be consumed by BQL as well.
>>> I just went over the patch again and I don't understand this comment.
>>> This patch only enabled BQL with tx napi.
>>>
>>> Thus there's no mode switching.
>>>
>>> What did I miss?
>> Consider the case:
>>
>>
>> TX NAPI is disabled:
>>
>> send N packets
>>
>> turn TX NAPI on:
>>
>> get tx interrupt
>>
>> BQL try to consume those packets when lead WARN for dql.
>>
>>
>> Thanks
> Can one really switch tx napi on and off? How?
> While root can change the napi_tx module parameter, I don't think
> that has any effect outside device probe time. What did I miss?
>
>
>

We support switch the mode through ethtool recently. See

commit 0c465be183c7c57a26446df6ea96d8676b865f92
Author: Jason Wang <jasowang@...hat.com>
Date:   Tue Oct 9 10:06:26 2018 +0800

     virtio_net: ethtool tx napi configuration

     Implement ethtool .set_coalesce (-C) and .get_coalesce (-c) handlers.
     Interrupt moderation is currently not supported, so these accept and
     display the default settings of 0 usec and 1 frame.

     Toggle tx napi through setting tx-frames. So as to not interfere
     with possible future interrupt moderation, value 1 means tx napi while
     value 0 means not.

     Only allow the switching when device is down for simplicity.

     Link: https://patchwork.ozlabs.org/patch/948149/
     Suggested-by: Jason Wang <jasowang@...hat.com>
     Signed-off-by: Willem de Bruijn <willemb@...gle.com>
     Signed-off-by: Jason Wang <jasowang@...hat.com>
     Signed-off-by: David S. Miller <davem@...emloft.net>

Thanks