Re: [dpdk-dev] [RFC PATCH 02/13] add vhost packed ring fast enqueue function

[Jason Wang <jasowang@redhat.com>]

On 2019/7/10 下午3:30, Liu, Yong wrote:
>
>> -----Original Message-----
>> From: Jason Wang [mailto:jasowang@redhat.com]
>> Sent: Wednesday, July 10, 2019 12:28 PM
>> To: Liu, Yong <yong.liu@intel.com>; Bie, Tiwei <tiwei.bie@intel.com>;
>> maxime.coquelin@redhat.com; dev@dpdk.org
>> Subject: Re: [dpdk-dev] [RFC PATCH 02/13] add vhost packed ring fast enqueue
>> function
>>
>>
>> On 2019/7/9 上午1:13, Marvin Liu wrote:
>>> In fast enqueue function, will first check whether descriptors are
>>> cache aligned. Fast enqueue function will check prerequisites in the
>>> beginning. Fast enqueue function do not support chained mbufs, normal
>>> function will handle that.
>>>
>>> Signed-off-by: Marvin Liu <yong.liu@intel.com>
>> Any reason for not letting compiler to unroll the loops?
>>
> Hi Jason,
> I'm not sure about how much compiler can help on unrolling loops as it can't know how much loops will create in one call.
> After force not using unroll-loop optimization by "-fno-unroll-loops", virtio_dev_rx_packed function size remained the same.
> So look like gcc unroll-loop optimization do not help here.


I meant something like "pragma GCC unroll N" just before the loop you 
want unrolled.

Thanks


>
> And fast enqueue function not only did unroll loop, it also checked cache alignment which can help performance in another side.
>
> Regards,
> Marvin
>
>> Thanks
>>