On Fri, Nov 24, 2017 at 01:01:08PM +0200, Roy Shterman wrote: > > > נשלח מה-iPhone שלי > > ב-24 בנוב׳ 2017, בשעה 12:03, Bruce Richardson > <bruce.richard...@intel.com> כתב/ה: > > >> On Fri, Nov 24, 2017 at 11:39:54AM +0200, roy wrote: > >> Thanks for your answer, but I cannot understand the dimension of the ring > >> and it is affected by the cache size. > >> > >>> On 24/11/17 11:30, Bruce Richardson wrote: > >>>> On Thu, Nov 23, 2017 at 11:05:11PM +0200, Roy Shterman wrote: > >>>> Hi, > >>>> > >>>> In the documentation it says that: > >>>> > >>>> * @param cache_size > >>>> * 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 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 > >>>> * faster than the multi-producer/consumer pool. The cache can be > >>>> * disabled if the cache_size argument is set to 0; it can be useful to > >>>> * avoid losing objects in cache. > >>>> > >>>> I wonder if someone can please explain the high-lightened sentence, how > >>>> the > >>>> cache size affects the objects inside the ring. > >>> It has no effects upon the objects themselves. Having a cache is > >>> strongly recommended for performance reasons. Accessing a shared ring > >>> for a mempool is very slow compared to pulling packets from a per-core > >>> cache. To test this you can run testpmd using different --mbcache > >>> parameters. > >> Still, I didn't understand the sentence from above: > >> > >> *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.* > >> > > > > This would be an artifact of the way in which the elements are taken > > from the pool ring. If a full cache-size burst of elements is not > > available in the ring, no elements from the ring are put in the cache. > > It just means that the pool can never fully be emptied. However, in most > > cases, even having the pool nearly empty indicates a problem, so > > practically I wouldn't be worried about this. > > > > But in case we tried to get cache size from pool and failed we will try to > get the number on objects defined in rte_mempool_get_bulk, so in case > rte_mempool_get() usage we will try to get one object out of the pool (ring) > so also if there isn't cache size in the ring itself each core can get 1 > object in each rte_memoool_get until the pool is empty, am I wrong? >
If there is no cache, you can always get all elements out of the ring by getting one at a time, yes.
