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

["Liu, Yong" <yong.liu@intel.com>]

> -----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. 

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

Regards,
Marvin

> Thanks
>