> From: Morten Brørup [mailto:m...@smartsharesystems.com] > Sent: Monday, 4 September 2023 10.44 > > This patch introduces the generic RTE_CACHE_GUARD macro into the EAL, and > replaces vaguely described empty cache lines in the rte_ring structure > with this macro. > > Although the implementation of the rte_ring structure assumes that the > hardware speculatively prefetches 1 cache line, this number can be changed > at build time by modifying RTE_CACHE_GUARD_LINES in rte_config.h. > > The background and the RFC was discussed in this thread: > http://inbox.dpdk.org/dev/98CBD80474FA8B44BF855DF32C47DC35D87B39@smartserver.s > martshare.dk/ > > Signed-off-by: Morten Brørup <m...@smartsharesystems.com> > --- > config/rte_config.h | 1 + > lib/eal/include/rte_common.h | 13 +++++++++++++ > lib/ring/rte_ring_core.h | 6 +++--- > 3 files changed, 17 insertions(+), 3 deletions(-) > > diff --git a/config/rte_config.h b/config/rte_config.h > index 400e44e3cf..cfdf787724 100644 > --- a/config/rte_config.h > +++ b/config/rte_config.h > @@ -37,6 +37,7 @@ > #define RTE_MAX_TAILQ 32 > #define RTE_LOG_DP_LEVEL RTE_LOG_INFO > #define RTE_MAX_VFIO_CONTAINERS 64 > +#define RTE_CACHE_GUARD_LINES 1 > > /* bsd module defines */ > #define RTE_CONTIGMEM_MAX_NUM_BUFS 64 > diff --git a/lib/eal/include/rte_common.h b/lib/eal/include/rte_common.h > index 771c70f2c8..daf1866a32 100644 > --- a/lib/eal/include/rte_common.h > +++ b/lib/eal/include/rte_common.h > @@ -527,6 +527,19 @@ rte_is_aligned(const void * const __rte_restrict ptr, > const unsigned int align) > /** Force minimum cache line alignment. */ > #define __rte_cache_min_aligned __rte_aligned(RTE_CACHE_LINE_MIN_SIZE) > > +#define _RTE_CACHE_GUARD_HELPER2(unique) \ > + char cache_guard_ ## unique[RTE_CACHE_LINE_SIZE * > RTE_CACHE_GUARD_LINES] \ > + __rte_cache_aligned > +#define _RTE_CACHE_GUARD_HELPER1(unique) _RTE_CACHE_GUARD_HELPER2(unique) > +/** > + * Empty cache lines, to guard against false sharing-like effects > + * on systems with a next-N-lines hardware prefetcher. > + * > + * Use as spacing between data accessed by different lcores, > + * to prevent cache thrashing on hardware with speculative prefetching. > + */ > +#define RTE_CACHE_GUARD _RTE_CACHE_GUARD_HELPER1(__COUNTER__) > + > /*********** PA/IOVA type definitions ********/ > > /** Physical address */ > diff --git a/lib/ring/rte_ring_core.h b/lib/ring/rte_ring_core.h > index d1e59bf9ad..327fdcf28f 100644 > --- a/lib/ring/rte_ring_core.h > +++ b/lib/ring/rte_ring_core.h > @@ -126,7 +126,7 @@ struct rte_ring { > uint32_t mask; /**< Mask (size-1) of ring. */ > uint32_t capacity; /**< Usable size of ring */ > > - char pad0 __rte_cache_aligned; /**< empty cache line */ > + RTE_CACHE_GUARD; > > /** Ring producer status. */ > union { > @@ -135,7 +135,7 @@ struct rte_ring { > struct rte_ring_rts_headtail rts_prod; > } __rte_cache_aligned; > > - char pad1 __rte_cache_aligned; /**< empty cache line */ > + RTE_CACHE_GUARD; > > /** Ring consumer status. */ > union { > @@ -144,7 +144,7 @@ struct rte_ring { > struct rte_ring_rts_headtail rts_cons; > } __rte_cache_aligned; > > - char pad2 __rte_cache_aligned; /**< empty cache line */ > + RTE_CACHE_GUARD; > }; > > #define RING_F_SP_ENQ 0x0001 /**< The default enqueue is "single-producer". > */ > -- > 2.17.1
I asked Mattias Rönnblom in the RFC discussion thread to ACK this patch, which he then did [1], so I'm copying his ACK here for patchwork to see. [1]: http://inbox.dpdk.org/dev/66b862bc-ca22-02da-069c-a82c2d52e...@lysator.liu.se/ Acked-by: Mattias Rönnblom <mattias.ronnb...@ericsson.com>
