netdev - Re: [PATCH net-next v5 0/4] net: vhost: improve performance when enable busyloop

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Date:   Thu, 12 Jul 2018 13:21:03 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     Tonghao Zhang <xiangxia.m.yue@...il.com>,
        makita.toshiaki@....ntt.co.jp,
        virtualization@...ts.linux-foundation.org,
        Linux Kernel Network Developers <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next v5 0/4] net: vhost: improve performance when
 enable busyloop



On 2018年07月12日 11:34, Michael S. Tsirkin wrote:
> On Thu, Jul 12, 2018 at 11:26:12AM +0800, Jason Wang wrote:
>>
>> On 2018年07月11日 19:59, Michael S. Tsirkin wrote:
>>> On Wed, Jul 11, 2018 at 01:12:59PM +0800, Jason Wang wrote:
>>>> On 2018年07月11日 11:49, Tonghao Zhang wrote:
>>>>> On Wed, Jul 11, 2018 at 10:56 AM Jason Wang <jasowang@...hat.com> wrote:
>>>>>> On 2018年07月04日 12:31, xiangxia.m.yue@...il.com wrote:
>>>>>>> From: Tonghao Zhang <xiangxia.m.yue@...il.com>
>>>>>>>
>>>>>>> This patches improve the guest receive and transmit performance.
>>>>>>> On the handle_tx side, we poll the sock receive queue at the same time.
>>>>>>> handle_rx do that in the same way.
>>>>>>>
>>>>>>> For more performance report, see patch 4.
>>>>>>>
>>>>>>> v4 -> v5:
>>>>>>> fix some issues
>>>>>>>
>>>>>>> v3 -> v4:
>>>>>>> fix some issues
>>>>>>>
>>>>>>> v2 -> v3:
>>>>>>> This patches are splited from previous big patch:
>>>>>>> http://patchwork.ozlabs.org/patch/934673/
>>>>>>>
>>>>>>> Tonghao Zhang (4):
>>>>>>>       vhost: lock the vqs one by one
>>>>>>>       net: vhost: replace magic number of lock annotation
>>>>>>>       net: vhost: factor out busy polling logic to vhost_net_busy_poll()
>>>>>>>       net: vhost: add rx busy polling in tx path
>>>>>>>
>>>>>>>      drivers/vhost/net.c   | 108 ++++++++++++++++++++++++++++----------------------
>>>>>>>      drivers/vhost/vhost.c |  24 ++++-------
>>>>>>>      2 files changed, 67 insertions(+), 65 deletions(-)
>>>>>>>
>>>>>> Hi, any progress on the new version?
>>>>>>
>>>>>> I plan to send a new series of packed virtqueue support of vhost. If you
>>>>>> plan to send it soon, I can wait. Otherwise, I will send my series.
>>>>> I rebase the codes. and find there is no improvement anymore, the
>>>>> patches of  makita  may solve the problem. jason you may send your
>>>>> patches, and I will do some research on busypoll.
>>>> I see. Maybe you can try some bi-directional traffic.
>>>>
>>>> Btw, lots of optimizations could be done for busy polling. E.g integrating
>>>> with host NAPI busy polling or a 100% busy polling vhost_net. You're welcome
>>>> to work or propose new ideas.
>>>>
>>>> Thanks
>>> It seems clear we do need adaptive polling.
>> Yes.
>>
>>>    The difficulty with NAPI
>>> polling is it can't access guest memory easily. But maybe
>>> get_user_pages on the polled memory+NAPI polling can work.
>> You mean something like zerocopy? Looks like we can do busy polling without
>> it. I mean something like https://patchwork.kernel.org/patch/8707511/.
>>
>> Thanks
> How does this patch work? vhost_vq_avail_empty can sleep,
> you are calling it within an rcu read side critical section.

Ok, I get your meaning. I have patches to access vring through 
get_user_pages + vmap() which should help here. (And it increase PPS 
about 10%-20%).

>
> That's not the only problem btw, another one is that the
> CPU time spent polling isn't accounted with the VM.


Yes, but it's not the 'issue' of this patch. And I believe cgroup can help?

Thanks

>
>>>>>> Thanks