On 02/25/2014 03:53 PM, Qin Chuanyu wrote:
> On 2014/2/25 15:38, Jason Wang wrote:
>> On 02/25/2014 02:55 PM, Qin Chuanyu wrote:
>>> guest kick vhost base on vring flag status and get perfermance
>>> improved,
>>> vhost_zerocopy_callback could do this in the same way, as
>>> virtqueue_enable_cb need one more check after change the status of
>>> avail_ring flags, vhost also do the same thing after
>>> vhost_enable_notify
>>>
>>> test result list as below:
>>> guest and host: suse11sp3, netperf, intel 2.4GHz
>>> +-------+----------+---------+----------+---------+
>>> | | old | new |
>>> +-------+----------+---------+----------+---------+
>>> | UDP | Gbit/s | PPS | Gbit/s | PPS |
>>> | 256 | 0.74805 | 321309 | 0.77933 | 334743 |
>>> | 512 | 1.42 | 328475 | 1.44 | 333550 |
>>> | 1024 | 2.79 | 334426 | 2.81 | 336986 |
>>> | 1460 | 3.71 | 316215 | 4.02 | 342325 |
>>> +-------+----------+---------+----------+---------+
>>
>> Looks good, do you have cpu utilization number?
> +------+----------+--------+----------+--------+--------+---------+
> | | old | new |
> +------+----------+--------+----------+--------+--------+---------+
> | UDP | Gbit/s | PPS |CPU idle% | Gbit/s | PPS |CPU idle%|
> | 256 | 0.74805 | 321309 | 87.16 | 0.77933| 334743 | 90.71 |
> | 512 | 1.42 | 328475 | 87.03 | 1.44 | 333550 | 90.43 |
> | 1024 | 2.79 | 334426 | 89.09 | 2.81 | 336986 | 89.55 |
> | 1460 | 3.71 | 316215 | 87.53 | 4.02 | 342325 | 89.58 |
> +------+----------+--------+----------+--------+--------+---------+
> after change, less cpu has been used.
Thanks
>>>
>>> Signed-off-by: Chuanyu Qin <qinchuanyu@xxxxxxxxxx>
>>> ---
>>> drivers/vhost/net.c | 10 +++++++++-
>>> 1 files changed, 9 insertions(+), 1 deletions(-)
>>>
>>> diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
>>> index a0fa5de..9bc0a15 100644
>>> --- a/drivers/vhost/net.c
>>> +++ b/drivers/vhost/net.c
>>> @@ -322,7 +322,9 @@ static void vhost_zerocopy_callback(struct
>>> ubuf_info *ubuf, bool success)
>>> * (the value 16 here is more or less arbitrary, it's tuned to
>>> trigger
>>> * less than 10% of times).
>>> */
>>> - if (cnt <= 1 || !(cnt % 16))
>>> + smp_rmb();
>>
>> Better add a comment to explain why this is needed.
>>
>> Looks like what you need is a smp_mb() here to make sure the len is
>> updated before testing vq->used_flags?
> I wanner make sure the used_flags is updated, is smp_rmb() enough?
> or a smp_mb() is needed?
used_flags was guaranteed to be updated after smp_mb() in
vhost_enable_notify(). And vhost_net_ubuf_put() does a
atomic_sub_return() which implements memory barrier. So looks like
there's no need for an extra one.
>>> + if ((!(vq->used_flags & VRING_USED_F_NO_NOTIFY))
>>> + && (cnt <= 1 || !(cnt % 16)))
>>> vhost_poll_queue(&vq->poll);
>>>
>>> rcu_read_unlock_bh();
>>> @@ -386,6 +388,12 @@ static void handle_tx(struct vhost_net *net)
>>> vhost_disable_notify(&net->dev, vq);
>>> continue;
>>> }
>>> + /* there might skb been freed between last
>>> + * vhost_zerocopy_signal_used and vhost_enable_notify,
>>> + * so one more check is needed.
>>> + */
>>> + if (zcopy)
>>> + vhost_zerocopy_signal_used(net, vq);
>>> break;
>>> }
>>> if (in) {
>>
>>
>> .
>>
>
>
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