Re: [Linux-kernel-mentees][PATCH 0/2] reorder members of structures in virtio_net for optimization

[Michael S. Tsirkin]

On Fri, Oct 02, 2020 at 07:06:38PM -0700, David Miller wrote:
> From: Anant Thazhemadam <anant.thazhemadam@xxxxxxxxx>
> Date: Wed, 30 Sep 2020 10:47:20 +0530
> 
> > The structures virtnet_info and receive_queue have byte holes in 
> > middle, and their members could do with some rearranging 
> > (order-of-declaration wise) in order to overcome this.
> > 
> > Rearranging the members helps in:
> >   * elimination the byte holes in the middle of the structures
> >   * reduce the size of the structure (virtnet_info)
> >   * have more members stored in one cache line (as opposed to 
> >     unnecessarily crossing the cacheline boundary and spanning
> >     different cachelines)
> > 
> > The analysis was performed using pahole.
> > 
> > These patches may be applied in any order.
> 
> What effects do these changes have on performance?
> 
> The cache locality for various TX and RX paths could be effected.
> 
> I'm not applying these patches without some data on the performance
> impact.
> 
> Thank you.

Agree wholeheartedly.

-- 
MST