From: Jason Wang <jasowang@redhat.com>
To: Tonghao Zhang <xiangxia.m.yue@gmail.com>
Cc: makita.toshiaki@lab.ntt.co.jp, mst@redhat.com,
virtualization@lists.linux-foundation.org,
Linux Kernel Network Developers <netdev@vger.kernel.org>
Subject: Re: [PATCH net-next v7 3/4] net: vhost: factor out busy polling logic to vhost_net_busy_poll()
Date: Fri, 3 Aug 2018 11:07:18 +0800 [thread overview]
Message-ID: <fc4dc137-98de-2cee-4f41-e23ab4eb2492@redhat.com> (raw)
In-Reply-To: <CAMDZJNUMBYOVh+pzaykRq23ePqNR7BOA8wP_=i85-PXvwaxuBA@mail.gmail.com>
On 2018年08月03日 10:51, Tonghao Zhang wrote:
> On Thu, Aug 2, 2018 at 5:23 PM Jason Wang <jasowang@redhat.com> wrote:
>>
>>
>> On 2018年08月02日 16:41, Toshiaki Makita wrote:
>>> On 2018/08/02 17:18, Jason Wang wrote:
>>>> On 2018年08月01日 17:52, Tonghao Zhang wrote:
>>>>>> +static void vhost_net_busy_poll_check(struct vhost_net *net,
>>>>>> + struct vhost_virtqueue *rvq,
>>>>>> + struct vhost_virtqueue *tvq,
>>>>>> + bool rx)
>>>>>> +{
>>>>>> + struct socket *sock = rvq->private_data;
>>>>>> +
>>>>>> + if (rx)
>>>>>> + vhost_net_busy_poll_try_queue(net, tvq);
>>>>>> + else if (sock && sk_has_rx_data(sock->sk))
>>>>>> + vhost_net_busy_poll_try_queue(net, rvq);
>>>>>> + else {
>>>>>> + /* On tx here, sock has no rx data, so we
>>>>>> + * will wait for sock wakeup for rx, and
>>>>>> + * vhost_enable_notify() is not needed. */
>>>>> A possible case is we do have rx data but guest does not refill the rx
>>>>> queue. In this case we may lose notifications from guest.
>>>> Yes, should consider this case. thanks.
>>> I'm a bit confused. Isn't this covered by the previous
>>> "else if (sock && sk_has_rx_data(...))" block?
>> The problem is it does nothing if vhost_vq_avail_empty() is true and
>> vhost_enble_notify() is false.
>>
>>>>>>> +
>>>>>>> + cpu_relax();
>>>>>>> + }
>>>>>>> +
>>>>>>> + preempt_enable();
>>>>>>> +
>>>>>>> + if (!rx)
>>>>>>> + vhost_net_enable_vq(net, vq);
>>>>>> No need to enable rx virtqueue, if we are sure handle_rx() will be
>>>>>> called soon.
>>>>> If we disable rx virtqueue in handle_tx and don't send packets from
>>>>> guest anymore(handle_tx is not called), so we can wake up for sock rx.
>>>>> so the network is broken.
>>>> Not sure I understand here. I mean is we schedule work for handle_rx(),
>>>> there's no need to enable it since handle_rx() will do this for us.
>>> Looks like in the last "else" block in vhost_net_busy_poll_check() we
>>> need to enable vq since in that case we have no rx data and handle_rx()
>>> is not scheduled.
>>>
>> Yes.
> So we will use the vhost_has_work() to check whether or not the
> handle_rx is scheduled ?
> If we use the vhost_has_work(), the work in the dev work_list may be
> rx work, or tx work, right ?
Yes. We can add a boolean to record whether or not we've called
vhost_poll_queue() for rvq. And avoid calling vhost_net_enable_vq() if
it was true.
So here's the needed changes:
1) Split the wakeup disabling to another patch
2) Squash the vhost_net_busy_poll_try_queue() and
vhost_net_busy_poll_check() into vhost_net_busy_poll() and reduce
duplicated checks.
3) If possible, rename the boolean rx in vhost_net_busy_poll() to
poll_rx, this makes code more readable.
Thanks
>> Thanks
next prev parent reply other threads:[~2018-08-03 5:01 UTC|newest]
Thread overview: 37+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-08-01 3:00 [PATCH net-next v7 0/4] net: vhost: improve performance when enable busyloop xiangxia.m.yue
2018-08-01 3:00 ` [PATCH net-next v7 1/4] net: vhost: lock the vqs one by one xiangxia.m.yue
2018-08-01 3:00 ` [PATCH net-next v7 2/4] net: vhost: replace magic number of lock annotation xiangxia.m.yue
2018-08-01 3:00 ` xiangxia.m.yue
2018-08-01 3:00 ` [PATCH net-next v7 3/4] net: vhost: factor out busy polling logic to vhost_net_busy_poll() xiangxia.m.yue
2018-08-01 6:01 ` Jason Wang
2018-08-01 9:52 ` Tonghao Zhang
2018-08-02 8:18 ` Jason Wang
2018-08-02 8:41 ` Toshiaki Makita
2018-08-02 9:23 ` Jason Wang
2018-08-02 9:57 ` Toshiaki Makita
2018-08-03 2:38 ` Jason Wang
2018-08-03 2:38 ` Jason Wang
2018-08-03 2:51 ` Tonghao Zhang
2018-08-03 2:51 ` Tonghao Zhang
2018-08-03 3:07 ` Jason Wang
2018-08-03 3:07 ` Jason Wang [this message]
2018-08-03 3:24 ` Tonghao Zhang
2018-08-03 3:40 ` Toshiaki Makita
2018-08-03 4:14 ` Tonghao Zhang
2018-08-03 4:25 ` Toshiaki Makita
2018-08-03 4:14 ` Tonghao Zhang
2018-08-03 3:43 ` Jason Wang
2018-08-03 3:43 ` Jason Wang
2018-08-03 4:04 ` Tonghao Zhang
2018-08-03 5:07 ` Jason Wang
2018-08-03 5:25 ` Toshiaki Makita
2018-08-03 3:24 ` Tonghao Zhang
2018-08-03 3:07 ` Jason Wang
2018-08-03 3:32 ` Toshiaki Makita
2018-08-03 3:44 ` Jason Wang
2018-08-03 3:44 ` Jason Wang
2018-08-03 3:07 ` Jason Wang
2018-08-02 8:18 ` Jason Wang
2018-08-01 3:00 ` xiangxia.m.yue
2018-08-01 3:00 ` [PATCH net-next v7 4/4] net: vhost: add rx busy polling in tx path xiangxia.m.yue
2018-08-01 3:00 ` xiangxia.m.yue
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