From: Andrew Rybchenko <andrew.rybchenko@oktetlabs.ru>
To: "Morten Brørup" <mb@smartsharesystems.com>,
"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 17:51:46 +0300 [thread overview]
Message-ID: <c87c72cb-2623-387c-e5cf-c82b460a6cb9@oktetlabs.ru> (raw)
In-Reply-To: <98CBD80474FA8B44BF855DF32C47DC35D873B6@smartserver.smartshare.dk>
On 10/9/22 17:31, Morten Brørup wrote:
>> 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;
I think aligning objs on cacheline should be a separate patch.
>
> With or without the above suggested optimization...
>
> Reviewed-by: Morten Brørup <mb@smartsharesystems.com>
>
next prev parent reply other threads:[~2022-10-09 14:51 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
2022-10-09 14:51 ` Andrew Rybchenko [this message]
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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