RE: Ring library optimization idea

[Konstantin Ananyev <konstantin.ananyev@huawei.com>]

Hi Morten,

> > Most of the fast path ring library functions access the two cache lines containing
> > respectively the r->prod and r->cons structures.
> >
> > Some of the fast path functions also have to fetch r->capacity and r->mask,
> > which reside in another cache line.
> >
> > What do you think about adding shadow variables of r->capacity and r->mask
> > to the same cache line as r->prod, to improve ring library performance (by
> > avoiding having to read a third cache line) when under CPU cache pressure?
> Agree with the idea. I am not sure about the performance as these are read-only data. IMO, we should not worry about it as it saves
> one cache line (but we do not need to measure the performance). They will occupy 12B, but I do not see how we will occupy the
> entire 64B of the cacheline in the near future.
> 
> Also, the shadow variables need to be part of both r->prod and r->cons.

Personally, I think that for majority of cases the perf gain with be either tiny or none.
From other side, I don't see any harm with that approach, as Honnapa said, we
do should have space for that in prod/cons cache-lines.
So, no objections from me in general.
Thanks
Konstantin