On 18/05/15 15:13, Ananyev, Konstantin wrote: > > >> -----Original Message----- >> From: Zoltan Kiss [mailto:zoltan.kiss at linaro.org] >> Sent: Monday, May 18, 2015 2:31 PM >> To: Ananyev, Konstantin; dev at dpdk.org >> Subject: Re: [dpdk-dev] [PATCH] mempool: limit cache_size >> >> >> >> On 18/05/15 14:14, Ananyev, Konstantin wrote: >>> >>> >>>> -----Original Message----- >>>> From: Zoltan Kiss [mailto:zoltan.kiss at linaro.org] >>>> Sent: Monday, May 18, 2015 1:50 PM >>>> To: Ananyev, Konstantin; dev at dpdk.org >>>> Subject: Re: [dpdk-dev] [PATCH] mempool: limit cache_size >>>> >>>> >>>> >>>> On 18/05/15 13:41, Ananyev, Konstantin wrote: >>>>> >>>>> >>>>>> -----Original Message----- >>>>>> From: dev [mailto:dev-bounces at dpdk.org] On Behalf Of Zoltan Kiss >>>>>> Sent: Monday, May 18, 2015 1:28 PM >>>>>> To: dev at dpdk.org >>>>>> Subject: Re: [dpdk-dev] [PATCH] mempool: limit cache_size >>>>>> >>>>>> Hi, >>>>>> >>>>>> Any opinion on this patch? >>>>>> >>>>>> Regards, >>>>>> >>>>>> Zoltan >>>>>> >>>>>> On 13/05/15 19:59, Zoltan Kiss wrote: >>>>>>> Otherwise cache_flushthresh can be bigger than n, and >>>>>>> a consumer can starve others by keeping every element >>>>>>> either in use or in the cache. >>>>>>> >>>>>>> Signed-off-by: Zoltan Kiss <zoltan.kiss at linaro.org> >>>>>>> --- >>>>>>> lib/librte_mempool/rte_mempool.c | 3 ++- >>>>>>> lib/librte_mempool/rte_mempool.h | 2 +- >>>>>>> 2 files changed, 3 insertions(+), 2 deletions(-) >>>>>>> >>>>>>> diff --git a/lib/librte_mempool/rte_mempool.c >>>>>>> b/lib/librte_mempool/rte_mempool.c >>>>>>> index cf7ed76..ca6cd9c 100644 >>>>>>> --- a/lib/librte_mempool/rte_mempool.c >>>>>>> +++ b/lib/librte_mempool/rte_mempool.c >>>>>>> @@ -440,7 +440,8 @@ rte_mempool_xmem_create(const char *name, unsigned >>>>>>> n, unsigned elt_size, >>>>>>> mempool_list = RTE_TAILQ_CAST(rte_mempool_tailq.head, >>>>>>> rte_mempool_list); >>>>>>> >>>>>>> /* asked cache too big */ >>>>>>> - if (cache_size > RTE_MEMPOOL_CACHE_MAX_SIZE) { >>>>>>> + if (cache_size > RTE_MEMPOOL_CACHE_MAX_SIZE || >>>>>>> + (uint32_t) cache_size * CACHE_FLUSHTHRESH_MULTIPLIER > n) { >>>>>>> rte_errno = EINVAL; >>>>>>> return NULL; >>>>>>> } >>>>> >>>>> Why just no 'cache_size > n' then? >>>> >>>> The commit message says: "Otherwise cache_flushthresh can be bigger than >>>> n, and a consumer can starve others by keeping every element either in >>>> use or in the cache." >>> >>> Ah yes, you right - your condition is more restrictive, which is better. >>> Though here you implicitly convert cache_size and n to floats and compare 2 >>> floats : >>> (uint32_t) cache_size * CACHE_FLUSHTHRESH_MULTIPLIER > n) >>> Shouldn't it be: >>> (uint32_t)(cache_size * CACHE_FLUSHTHRESH_MULTIPLIER) > n) >>> So we do conversion back to uint32_t compare to unsigned integers instead? >>> Same as below: >>> mp->cache_flushthresh = (uint32_t) >>> (cache_size * CACHE_FLUSHTHRESH_MULTIPLIER); >> >> To bring it further: how about ditching the whole cache_flushthresh >> member of the mempool structure, and use this: >> >> #define CACHE_FLUSHTHRESH(mp) (uint32_t)((mp)->cache_size * 1.5) > > That's quite expensive and I think would slow down mempool_put() quite a lot . > So I'd suggest we keep cache_flushthresh as it is. Ok, I have posted a v2 based on your suggestion. > >> >> Furthermore, do we want to expose the flush threshold multiplier through >> the config file? > > Hmm, my opinion is no - so far no one ask for that, > and as general tendency - we trying to reduce number of options in config > file. > Do you have any good justification when current value is not good enough?
Nothing special, just the arbitrary value choice seemed a bit odd. > Anyway, that probably could be a subject of another patch/discussion. > Konstantin > >> >>> ? >>> >>> In fact, as we use it more than once, it probably makes sense to create a >>> macro for it, >>> something like: >>> #define CALC_CACHE_FLUSHTHRESH(c) ((uint32_t)((c) * >>> CACHE_FLUSHTHRESH_MULTIPLIER) >>> >>> Or even >>> >>> #define CALC_CACHE_FLUSHTHRESH(c) ((typeof (c))((c) * >>> CACHE_FLUSHTHRESH_MULTIPLIER) >>> >>> >>> Konstantin >>> >>>> >>>>> Konstantin >>>>> >>>>>>> diff --git a/lib/librte_mempool/rte_mempool.h >>>>>>> b/lib/librte_mempool/rte_mempool.h >>>>>>> index 9001312..a4a9610 100644 >>>>>>> --- a/lib/librte_mempool/rte_mempool.h >>>>>>> +++ b/lib/librte_mempool/rte_mempool.h >>>>>>> @@ -468,7 +468,7 @@ typedef void (rte_mempool_ctor_t)(struct >>>>>>> rte_mempool *, void *); >>>>>>> * If cache_size is non-zero, the rte_mempool library will try to >>>>>>> * limit the accesses to the common lockless pool, by >>>>>>> maintaining a >>>>>>> * per-lcore object cache. This argument must be lower or equal >>>>>>> to >>>>>>> - * CONFIG_RTE_MEMPOOL_CACHE_MAX_SIZE. It is advised to choose >>>>>>> + * CONFIG_RTE_MEMPOOL_CACHE_MAX_SIZE and n / 1.5. It is advised to >>>>>>> choose >>>>>>> * cache_size to have "n modulo cache_size == 0": if this is >>>>>>> * not the case, some elements will always stay in the pool and >>>>>>> will >>>>>>> * never be used. The access to the per-lcore table is of course >>>>>>>
