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.*
And also does it mean that
if I'm sharing pool between different cores can it be that a core sees the
pool as empty although it has objects in it?
Yes, that can occur. You need to dimension the pool to take account of
your cache usage.
can you please elaborate more on this issue? I'm working with
multi-consumer multi-producer pools, in my understanding object can or
in lcore X cache or in ring.
Each core when looking for objects in pool (ring) is looking at
prod/cons head/tail so how can it be that the cache of different cores
affects this?
/Bruce
