Re: [dpdk-dev] [dpdk-stable] [PATCH v2 2/4] hash: add local cache for TSX region

[Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>]

> > >
> > > From: Yipeng Wang <yipeng1.wang@intel.com>
> > >
> > > This patch adds back the local cache when TSX support is turned on.
> > >
> > > When TSX is turned on, free key-data slot ring would be contended by
> > > various TSX regions. The purpose of this commit is to reduce
> > > possible memory collisions during key insertion.
> > >
> > > Signed-off-by: Yipeng Wang <yipeng1.wang@intel.com>
> > > Acked-by: Bruce Richardson <bruce.richardson@intel.com>
> > > ---
> > >  lib/librte_hash/rte_cuckoo_hash.c | 4 +++-
> > >  1 file changed, 3 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/lib/librte_hash/rte_cuckoo_hash.c
> > > b/lib/librte_hash/rte_cuckoo_hash.c
> > > index 76f5dc8..5d5f9f1 100644
> > > --- a/lib/librte_hash/rte_cuckoo_hash.c
> > > +++ b/lib/librte_hash/rte_cuckoo_hash.c
> > > @@ -180,8 +180,10 @@ struct rte_hash *
> > >  	}
> > >
> > >  	/* Check extra flags field to check extra options. */
> > > -	if (params->extra_flag &
> > > RTE_HASH_EXTRA_FLAGS_TRANS_MEM_SUPPORT)
> > > +	if (params->extra_flag &
> > > RTE_HASH_EXTRA_FLAGS_TRANS_MEM_SUPPORT) {
> > > +		use_local_cache = 1;
> > Do you see the issue even in the case of single writer? Enabling this flag
> creates local caches on all the data plane cores. This increases the memory
> usage for the single writer use case. Then there is 'writers on the control
> plane' use case, the requirement on hash_add rate is comparatively lower
> when compared to 'writers on the data plane'. The writers also are not pinned
> to any core as well. In this use case, I am not sure how much having a local
> cache matters.
> >
> > Enabling this flag effectively changes the free slot allocation from a ring to a
> stack data structure. Does it indicate that for single writer use case with TSX,
> the free slot (global) data structure should be a stack (rather than a ring)?
> 
> Is it blocking this patchset from entering in 18.11?
> If I understand well, there are some fixes for 18.11.
> 
I am fine with the other fixes in this patchset