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Date:   Thu, 12 Jul 2018 13:51:51 +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 13:24, Michael S. Tsirkin wrote:
> On Thu, Jul 12, 2018 at 01:21:03PM +0800, Jason Wang wrote:
>>
>> 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%).
> Remember you must mark it as dirty on unpin too ...

Ok.

>
>
>>> 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.
> Yes it is. polling within thread context accounts CPU correctly.
>
>> And I believe cgroup can help?
>>
>> Thanks
>
> cgroups are what's broken by polling in irq context.

But I think the NAPI busy polling is still done in process context.

Thanks

>
>>>>>>>> Thanks

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