netdev - Re: [PATCH net-next RFC 2/4] virtio-net: transmit napi

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Date:   Mon, 6 Mar 2017 14:43:50 -0500
From:   Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     David Miller <davem@...emloft.net>,
        Jason Wang <jasowang@...hat.com>,
        Network Development <netdev@...r.kernel.org>,
        Willem de Bruijn <willemb@...gle.com>
Subject: Re: [PATCH net-next RFC 2/4] virtio-net: transmit napi

On Mon, Mar 6, 2017 at 2:33 PM, Michael S. Tsirkin <mst@...hat.com> wrote:
> On Mon, Mar 06, 2017 at 10:55:22AM -0800, David Miller wrote:
>> From: Willem de Bruijn <willemdebruijn.kernel@...il.com>
>> Date: Mon, 6 Mar 2017 12:50:19 -0500
>>
>> >>>   drivers/net/virtio_net.c | 73
>> >>> ++++++++++++++++++++++++++++++++++++++++--------
>> >>>   1 file changed, 61 insertions(+), 12 deletions(-)
>> >>>
>> >>> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
>> >>> index 8c21e9a4adc7..9a9031640179 100644
>> >>> --- a/drivers/net/virtio_net.c
>> >>> +++ b/drivers/net/virtio_net.c
>> >>> @@ -33,6 +33,8 @@
>> >>>   static int napi_weight = NAPI_POLL_WEIGHT;
>> >>>   module_param(napi_weight, int, 0444);
>> >>>   +static int napi_tx_weight = NAPI_POLL_WEIGHT;
>> >>> +
>> >>
>> >>
>> >> Maybe we should use module_param for this? Or in the future, use
>> >> tx-frames-irq for a per-device configuration.
>> >
>> > This option should eventually just go away, and napi tx become the
>> > standard mode.
>> >
>> > In the short term, while we evaluate it on varied workloads, a
>> > module_param sounds good to me. In general that is frowned
>> > upon, as it leads to different configuration interfaces for each
>> > device driver. But that should not be a concern in this limited
>> > case.
>>
>> In any event, do we really need a TX weight at all?
>>
>> I guess you tried this, but why doesn't it not work to just do
>> all TX work unconditionally in a NAPI poll pass?  This is how
>> we encourage all NIC drivers to handle this.
>
> This seems to be more or less what this driver does already.
> So I suspect it can just ignore the weight.

Okay. Then we still need a boolean to toggle tx napi until we're
sure that the old path can be deprecated.