RE: [PATCH] ring: add cache guard after ring elements table

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

> > > Added cache guard after the table holding the ring elements, to avoid
> > > false sharing conflicts caused by next-line hardware prefetchers when
> > > accessing elements at the end of the ring table.
> >
> > I don't see any harm with it, and in theory it might help in some
> > cases...
> > Though I wonder how real is that problem?
> > Did you ever observe such contention to happen?
> 
> I never observed a problem with this.
> The risk of contention depends on what is allocated in the memory after the ring.
> Which is application specific.
> 
> It seems like a purely theoretical issue, but should be fixed anyway, to eliminate
> that risk.

Ok, as I said I see no harm with it.
Should we document this change somewhere? RN or PG?
Acked-by: Konstantin Ananyev <konstantin.ananyev@huawei.com>

> >
> > > Signed-off-by: Morten Brørup <mb@smartsharesystems.com>
> > > ---
> > >  lib/ring/rte_ring.c | 3 +++
> > >  1 file changed, 3 insertions(+)
> > >
> > > diff --git a/lib/ring/rte_ring.c b/lib/ring/rte_ring.c
> > > index f10050a1c4..9ccc62cd42 100644
> > > --- a/lib/ring/rte_ring.c
> > > +++ b/lib/ring/rte_ring.c
> > > @@ -73,8 +73,11 @@ rte_ring_get_memsize_elem(unsigned int esize,
> > unsigned
> > > int count)
> > >  		return -EINVAL;
> > >  	}
> > >
> > > +	static_assert(sizeof(struct rte_ring) ==
> > > RTE_CACHE_LINE_ROUNDUP(sizeof(struct rte_ring)),
> > > +			"Size of struct rte_ring not cache line aligned");
> > >  	sz = sizeof(struct rte_ring) + (ssize_t)count * esize;
> > >  	sz = RTE_ALIGN(sz, RTE_CACHE_LINE_SIZE);
> > > +	sz += RTE_CACHE_GUARD_LINES * RTE_CACHE_LINE_SIZE;
> > >  	return sz;
> > >  }
> > >
> > > --
> > > 2.43.0