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From: "Morten Brørup" <mb@smartsharesystems.com>
To: "Andrew Rybchenko" <andrew.rybchenko@oktetlabs.ru>,
	"Olivier Matz" <olivier.matz@6wind.com>
Cc: <dev@dpdk.org>, "Bruce Richardson" <bruce.richardson@intel.com>
Subject: RE: [PATCH v6 3/4] mempool: fix cache flushing algorithm
Date: Sun, 9 Oct 2022 16:31:50 +0200	[thread overview]
Message-ID: <98CBD80474FA8B44BF855DF32C47DC35D873B6@smartserver.smartshare.dk> (raw)
In-Reply-To: <20221009133737.795377-4-andrew.rybchenko@oktetlabs.ru>

> From: Andrew Rybchenko [mailto:andrew.rybchenko@oktetlabs.ru]
> Sent: Sunday, 9 October 2022 15.38
> 
> From: Morten Brørup <mb@smartsharesystems.com>
> 
> Fix the rte_mempool_do_generic_put() caching flushing algorithm to
> keep hot objects in cache instead of cold ones.
> 
> The algorithm was:
>  1. Add the objects to the cache.
>  2. Anything greater than the cache size (if it crosses the cache flush
>     threshold) is flushed to the backend.
> 
> Please note that the description in the source code said that it kept
> "cache min value" objects after flushing, but the function actually
> kept
> the cache full after flushing, which the above description reflects.
> 
> Now, the algorithm is:
>  1. If the objects cannot be added to the cache without crossing the
>     flush threshold, flush some cached objects to the backend to
>     free up required space.
>  2. Add the objects to the cache.
> 
> The most recent (hot) objects were flushed, leaving the oldest (cold)
> objects in the mempool cache. The bug degraded performance, because
> flushing prevented immediate reuse of the (hot) objects already in
> the CPU cache.  Now, the existing (cold) objects in the mempool cache
> are flushed before the new (hot) objects are added the to the mempool
> cache.
> 
> Since nearby code is touched anyway fix flush threshold comparison
> to do flushing if the threshold is really exceed, not just reached.
> I.e. it must be "len > flushthresh", not "len >= flushthresh".
> Consider a flush multiplier of 1 instead of 1.5; the cache would be
> flushed already when reaching size objects, not when exceeding size
> objects. In other words, the cache would not be able to hold "size"
> objects, which is clearly a bug. The bug could degraded performance
> due to premature flushing.
> 
> Since we never exceed flush threshold now, cache size in the mempool
> may be decreased from RTE_MEMPOOL_CACHE_MAX_SIZE * 3 to
> RTE_MEMPOOL_CACHE_MAX_SIZE * 2. In fact it could be
> CALC_CACHE_FLUSHTHRESH(RTE_MEMPOOL_CACHE_MAX_SIZE), but flush
> threshold multiplier is internal.
> 
> Signed-off-by: Morten Brørup <mb@smartsharesystems.com>
> Signed-off-by: Andrew Rybchenko <andrew.rybchenko@oktetlabs.ru>
> ---

[...]

> --- a/lib/mempool/rte_mempool.h
> +++ b/lib/mempool/rte_mempool.h
> @@ -90,7 +90,7 @@ struct rte_mempool_cache {
>  	 * Cache is allocated to this size to allow it to overflow in
> certain
>  	 * cases to avoid needless emptying of cache.
>  	 */
> -	void *objs[RTE_MEMPOOL_CACHE_MAX_SIZE * 3]; /**< Cache objects */
> +	void *objs[RTE_MEMPOOL_CACHE_MAX_SIZE * 2]; /**< Cache objects */
>  } __rte_cache_aligned;

How much are we allowed to break the ABI here?

This patch reduces the size of the structure by removing a now unused part at the end, which should be harmless.

If we may also move the position of the objs array, I would add __rte_cache_aligned to the objs array. It makes no difference in the general case, but if get/put operations are always 32 objects, it will reduce the number of memory (or last level cache) accesses from five to four 64 B cache lines for every get/put operation.

	uint32_t len;	      /**< Current cache count */
-	/*
-	 * Cache is allocated to this size to allow it to overflow in certain
-	 * cases to avoid needless emptying of cache.
-	 */
-	void *objs[RTE_MEMPOOL_CACHE_MAX_SIZE * 3]; /**< Cache objects */
+	/**
+	 * Cache objects
+	 *
+	 * Cache is allocated to this size to allow it to overflow in certain
+	 * cases to avoid needless emptying of cache.
+	 */
+	void *objs[RTE_MEMPOOL_CACHE_MAX_SIZE * 2] __rte_cache_aligned;
} __rte_cache_aligned;

With or without the above suggested optimization...

Reviewed-by: Morten Brørup <mb@smartsharesystems.com>


  reply	other threads:[~2022-10-09 14:31 UTC|newest]

Thread overview: 85+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-12-26 15:34 [RFC] mempool: rte_mempool_do_generic_get optimizations Morten Brørup
2022-01-06 12:23 ` [PATCH] mempool: optimize incomplete cache handling Morten Brørup
2022-01-06 16:55   ` Jerin Jacob
2022-01-07  8:46     ` Morten Brørup
2022-01-10  7:26       ` Jerin Jacob
2022-01-10 10:55         ` Morten Brørup
2022-01-14 16:36 ` [PATCH] mempool: fix get objects from mempool with cache Morten Brørup
2022-01-17 17:35   ` Bruce Richardson
2022-01-18  8:25     ` Morten Brørup
2022-01-18  9:07       ` Bruce Richardson
2022-01-24 15:38   ` Olivier Matz
2022-01-24 16:11     ` Olivier Matz
2022-01-28 10:22     ` Morten Brørup
2022-01-17 11:52 ` [PATCH] mempool: optimize put objects to " Morten Brørup
2022-01-19 14:52 ` [PATCH v2] mempool: fix " Morten Brørup
2022-01-19 15:03 ` [PATCH v3] " Morten Brørup
2022-01-24 15:39   ` Olivier Matz
2022-01-28  9:37     ` Morten Brørup
2022-02-02  8:14 ` [PATCH v2] mempool: fix get objects from " Morten Brørup
2022-06-15 21:18   ` Morten Brørup
2022-09-29 10:52     ` Morten Brørup
2022-10-04 12:57   ` Andrew Rybchenko
2022-10-04 15:13     ` Morten Brørup
2022-10-04 15:58       ` Andrew Rybchenko
2022-10-04 18:09         ` Morten Brørup
2022-10-06 13:43       ` Aaron Conole
2022-10-04 16:03   ` Morten Brørup
2022-10-04 16:36   ` Morten Brørup
2022-10-04 16:39   ` Morten Brørup
2022-02-02 10:33 ` [PATCH v4] mempool: fix mempool cache flushing algorithm Morten Brørup
2022-04-07  9:04   ` Morten Brørup
2022-04-07  9:14     ` Bruce Richardson
2022-04-07  9:26       ` Morten Brørup
2022-04-07 10:32         ` Bruce Richardson
2022-04-07 10:43           ` Bruce Richardson
2022-04-07 11:36             ` Morten Brørup
2022-10-04 20:01   ` Morten Brørup
2022-10-09 11:11   ` [PATCH 1/2] mempool: check driver enqueue result in one place Andrew Rybchenko
2022-10-09 11:11     ` [PATCH 2/2] mempool: avoid usage of term ring on put Andrew Rybchenko
2022-10-09 13:08       ` Morten Brørup
2022-10-09 13:14         ` Andrew Rybchenko
2022-10-09 13:01     ` [PATCH 1/2] mempool: check driver enqueue result in one place Morten Brørup
2022-10-09 13:19   ` [PATCH v4] mempool: fix mempool cache flushing algorithm Andrew Rybchenko
2022-10-04 12:53 ` [PATCH v3] mempool: fix get objects from mempool with cache Andrew Rybchenko
2022-10-04 14:42   ` Morten Brørup
2022-10-07 10:44 ` [PATCH v4] " Andrew Rybchenko
2022-10-08 20:56   ` Thomas Monjalon
2022-10-11 20:30     ` Copy-pasted code should be updated Morten Brørup
2022-10-11 21:47       ` Honnappa Nagarahalli
2022-10-30  8:44         ` Morten Brørup
2022-10-30 22:50           ` Honnappa Nagarahalli
2022-10-14 14:01     ` [PATCH v4] mempool: fix get objects from mempool with cache Olivier Matz
2022-10-09 13:37 ` [PATCH v6 0/4] mempool: fix mempool cache flushing algorithm Andrew Rybchenko
2022-10-09 13:37   ` [PATCH v6 1/4] mempool: check driver enqueue result in one place Andrew Rybchenko
2022-10-09 13:37   ` [PATCH v6 2/4] mempool: avoid usage of term ring on put Andrew Rybchenko
2022-10-09 13:37   ` [PATCH v6 3/4] mempool: fix cache flushing algorithm Andrew Rybchenko
2022-10-09 14:31     ` Morten Brørup [this message]
2022-10-09 14:51       ` Andrew Rybchenko
2022-10-09 15:08         ` Morten Brørup
2022-10-14 14:01           ` Olivier Matz
2022-10-14 15:57             ` Morten Brørup
2022-10-14 19:50               ` Olivier Matz
2022-10-15  6:57                 ` Morten Brørup
2022-10-18 16:32                   ` Jerin Jacob
2022-10-09 13:37   ` [PATCH v6 4/4] mempool: flush cache completely on overflow Andrew Rybchenko
2022-10-09 14:44     ` Morten Brørup
2022-10-14 14:01       ` Olivier Matz
2022-10-10 15:21   ` [PATCH v6 0/4] mempool: fix mempool cache flushing algorithm Thomas Monjalon
2022-10-11 19:26     ` Morten Brørup
2022-10-26 14:09     ` Thomas Monjalon
2022-10-26 14:26       ` Morten Brørup
2022-10-26 14:44         ` [PATCH] mempool: cache align mempool cache objects Morten Brørup
2022-10-26 19:44           ` Andrew Rybchenko
2022-10-27  8:34           ` Olivier Matz
2022-10-27  9:22             ` Morten Brørup
2022-10-27 11:42               ` Olivier Matz
2022-10-27 12:11                 ` Morten Brørup
2022-10-27 15:20                   ` Olivier Matz
2022-10-28  6:35           ` [PATCH v3 1/2] " Morten Brørup
2022-10-28  6:35             ` [PATCH v3 2/2] mempool: optimized debug statistics Morten Brørup
2022-10-28  6:41           ` [PATCH v4 1/2] mempool: cache align mempool cache objects Morten Brørup
2022-10-28  6:41             ` [PATCH v4 2/2] mempool: optimized debug statistics Morten Brørup
2022-10-30  9:09               ` Morten Brørup
2022-10-30  9:16                 ` Thomas Monjalon
2022-10-30  9:17             ` [PATCH v4 1/2] mempool: cache align mempool cache objects Thomas Monjalon

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