[PATCH v4 2/2] mempool: optimized debug statistics

[Morten Brørup]

> From: Morten Brørup [mailto:mb at smartsharesystems.com]
> Sent: Friday, 28 October 2022 08.42
> 
> When built with debug enabled (RTE_LIBRTE_MEMPOOL_DEBUG defined), the
> performance of mempools with caches is improved as follows.
> 
> Accessing objects in the mempool is likely to increment either the
> put_bulk and put_objs or the get_success_bulk and get_success_objs
> debug statistics counters.
> 
> By adding an alternative set of these counters to the mempool cache
> structure, accessing the dedicated debug statistics structure is
> avoided in
> the likely cases where these counters are incremented.
> 
> The trick here is that the cache line holding the mempool cache
> structure
> is accessed anyway, in order to update the "len" field. Updating some
> debug statistics counters in the same cache line has lower performance
> cost than accessing the debug statistics counters in the dedicated
> debug
> statistics structure, i.e. in another cache line.
> 
> Running mempool_perf_autotest on a VMware virtual server shows an avg.
> increase of 6.4 % in rate_persec for the tests with cache. (Only when
> built with debug enabled, obviously!)
> 
> For the tests without cache, the avg. increase in rate_persec is 0.8 %.
> I
> assume this is noise from the test environment.
> 
> v4:
> * Fix spelling and repeated word in commit message, caught by
> checkpatch.
> v3:
> * Try to fix git reference by making part of a series.
> * Add --in-reply-to v1 when sending email.
> v2:
> * Fix spelling and repeated word in commit message, caught by
> checkpatch.
> 
> Signed-off-by: Morten Brørup <mb at smartsharesystems.com>
> ---
>  lib/mempool/rte_mempool.c |  7 +++++
>  lib/mempool/rte_mempool.h | 55 +++++++++++++++++++++++++++++++--------
>  2 files changed, 51 insertions(+), 11 deletions(-)
> 
> diff --git a/lib/mempool/rte_mempool.c b/lib/mempool/rte_mempool.c
> index 21c94a2b9f..7b8c00a022 100644
> --- a/lib/mempool/rte_mempool.c
> +++ b/lib/mempool/rte_mempool.c
> @@ -1285,6 +1285,13 @@ rte_mempool_dump(FILE *f, struct rte_mempool
> *mp)
>  		sum.get_fail_objs += mp->stats[lcore_id].get_fail_objs;
>  		sum.get_success_blks += mp-
> >stats[lcore_id].get_success_blks;
>  		sum.get_fail_blks += mp->stats[lcore_id].get_fail_blks;
> +		/* Add the fast access statistics, if local caches exist */
> +		if (mp->cache_size != 0) {
> +			sum.put_bulk += mp->local_cache[lcore_id].put_bulk;
> +			sum.put_objs += mp->local_cache[lcore_id].put_objs;
> +			sum.get_success_bulk += mp-
> >local_cache[lcore_id].get_success_bulk;
> +			sum.get_success_objs += mp-
> >local_cache[lcore_id].get_success_objs;
> +		}
>  	}
>  	fprintf(f, "  stats:\n");
>  	fprintf(f, "    put_bulk=%"PRIu64"\n", sum.put_bulk);
> diff --git a/lib/mempool/rte_mempool.h b/lib/mempool/rte_mempool.h
> index 3725a72951..d84087bc92 100644
> --- a/lib/mempool/rte_mempool.h
> +++ b/lib/mempool/rte_mempool.h
> @@ -86,6 +86,14 @@ struct rte_mempool_cache {
>  	uint32_t size;	      /**< Size of the cache */
>  	uint32_t flushthresh; /**< Threshold before we flush excess
> elements */
>  	uint32_t len;	      /**< Current cache count */
> +#ifdef RTE_LIBRTE_MEMPOOL_DEBUG
> +	uint32_t unused;
> +	/* Fast access statistics, only for likely events */
> +	uint64_t put_bulk;             /**< Number of puts. */
> +	uint64_t put_objs;             /**< Number of objects
> successfully put. */
> +	uint64_t get_success_bulk;     /**< Successful allocation number.
> */
> +	uint64_t get_success_objs;     /**< Objects successfully
> allocated. */
> +#endif
>  	/**
>  	 * Cache objects
>  	 *
> @@ -1327,13 +1335,19 @@ rte_mempool_do_generic_put(struct rte_mempool
> *mp, void * const *obj_table,
>  {
>  	void **cache_objs;
> 
> +	/* No cache provided */
> +	if (unlikely(cache == NULL))
> +		goto driver_enqueue;
> +
> +#ifdef RTE_LIBRTE_MEMPOOL_DEBUG
>  	/* increment stat now, adding in mempool always success */
> -	RTE_MEMPOOL_STAT_ADD(mp, put_bulk, 1);
> -	RTE_MEMPOOL_STAT_ADD(mp, put_objs, n);
> +	cache->put_bulk += 1;
> +	cache->put_objs += n;
> +#endif
> 
> -	/* No cache provided or the request itself is too big for the
> cache */
> -	if (unlikely(cache == NULL || n > cache->flushthresh))
> -		goto driver_enqueue;
> +	/* The request is too big for the cache */
> +	if (unlikely(n > cache->flushthresh))
> +		goto driver_enqueue_stats_incremented;
> 
>  	/*
>  	 * The cache follows the following algorithm:
> @@ -1358,6 +1372,12 @@ rte_mempool_do_generic_put(struct rte_mempool
> *mp, void * const *obj_table,
> 
>  driver_enqueue:
> 
> +	/* increment stat now, adding in mempool always success */
> +	RTE_MEMPOOL_STAT_ADD(mp, put_bulk, 1);
> +	RTE_MEMPOOL_STAT_ADD(mp, put_objs, n);
> +
> +driver_enqueue_stats_incremented:
> +
>  	/* push objects to the backend */
>  	rte_mempool_ops_enqueue_bulk(mp, obj_table, n);
>  }
> @@ -1464,8 +1484,10 @@ rte_mempool_do_generic_get(struct rte_mempool
> *mp, void **obj_table,
>  	if (remaining == 0) {
>  		/* The entire request is satisfied from the cache. */
> 
> -		RTE_MEMPOOL_STAT_ADD(mp, get_success_bulk, 1);
> -		RTE_MEMPOOL_STAT_ADD(mp, get_success_objs, n);
> +#ifdef RTE_LIBRTE_MEMPOOL_DEBUG
> +		cache->get_success_bulk += 1;
> +		cache->get_success_objs += n;
> +#endif
> 
>  		return 0;
>  	}
> @@ -1494,8 +1516,10 @@ rte_mempool_do_generic_get(struct rte_mempool
> *mp, void **obj_table,
> 
>  	cache->len = cache->size;
> 
> -	RTE_MEMPOOL_STAT_ADD(mp, get_success_bulk, 1);
> -	RTE_MEMPOOL_STAT_ADD(mp, get_success_objs, n);
> +#ifdef RTE_LIBRTE_MEMPOOL_DEBUG
> +	cache->get_success_bulk += 1;
> +	cache->get_success_objs += n;
> +#endif
> 
>  	return 0;
> 
> @@ -1517,8 +1541,17 @@ rte_mempool_do_generic_get(struct rte_mempool
> *mp, void **obj_table,
>  		RTE_MEMPOOL_STAT_ADD(mp, get_fail_bulk, 1);
>  		RTE_MEMPOOL_STAT_ADD(mp, get_fail_objs, n);
>  	} else {
> -		RTE_MEMPOOL_STAT_ADD(mp, get_success_bulk, 1);
> -		RTE_MEMPOOL_STAT_ADD(mp, get_success_objs, n);
> +#ifdef RTE_LIBRTE_MEMPOOL_DEBUG
> +		if (likely(cache != NULL)) {
> +			cache->get_success_bulk += 1;
> +			cache->get_success_bulk += n;
> +		} else {
> +#endif
> +			RTE_MEMPOOL_STAT_ADD(mp, get_success_bulk, 1);
> +			RTE_MEMPOOL_STAT_ADD(mp, get_success_bulk, n);
> +#ifdef RTE_LIBRTE_MEMPOOL_DEBUG
> +		}
> +#endif
>  	}
> 
>  	return ret;
> --
> 2.17.1

I am retracting this second part of the patch series, and reopening the original patch instead. This second part is probably not going to make it to 22.11 anyway.

Instead, I am going to provide another patch series (after 22.11) to split the current RTE_LIBRTE_MEMPOOL_DEBUG define in two: RTE_LIBRTE_MEMPOOL_STATS for statistics, and RTE_LIBRTE_MEMPOOL_DEBUG for debugging. And then this patch can be added to the RTE_LIBRTE_MEMPOOL_STATS.

-Morten