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    SubjectRe: [PATCH RFC 1/2] virtio-net: bql support
    On Wed, Jan 02, 2019 at 11:30:11AM +0800, Jason Wang wrote:
    >
    > 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@redhat.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@redhat.com>
    >     Signed-off-by: Willem de Bruijn <willemb@google.com>
    >     Signed-off-by: Jason Wang <jasowang@redhat.com>
    >     Signed-off-by: David S. Miller <davem@davemloft.net>
    >
    > Thanks


    It's disabled when device is up - isn't that enough?

    --
    MST

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