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

["Morten Brørup" <mb@smartsharesystems.com>]

> From: Konstantin Ananyev [mailto:konstantin.ananyev@huawei.com]
> Sent: Thursday, 30 April 2026 19.22
> 
> Hi Morten,
> 
> > 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.

> 
> > 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