Re: [dpdk-stable] [dpdk-dev] [RFC v2 01/17] mempool: fix phys contig check if populate default skipped

[Andrew Rybchenko <arybchenko@solarflare.com>]

On 02/01/2018 12:09 PM, santosh wrote:
> On Thursday 01 February 2018 12:24 PM, Andrew Rybchenko wrote:
>> On 02/01/2018 08:05 AM, santosh wrote:
>>> On Wednesday 31 January 2018 10:15 PM, Olivier Matz wrote:
>>>> On Tue, Jan 23, 2018 at 01:15:56PM +0000, Andrew Rybchenko wrote:
>>>>> There is not specified dependency between rte_mempool_populate_default()
>>>>> and rte_mempool_populate_iova(). So, the second should not rely on the
>>>>> fact that the first adds capability flags to the mempool flags.
>>>>>
>>>>> Fixes: 65cf769f5e6a ("mempool: detect physical contiguous objects")
>>>>> Cc: stable@dpdk.org
>>>>>
>>>>> Signed-off-by: Andrew Rybchenko <arybchenko@solarflare.com>
>>>> Looks good to me. I agree it's strange that the mp->flags are
>>>> updated with capabilities only in rte_mempool_populate_default().
>>>> I see that this behavior is removed later in the patchset since the
>>>> get_capa() is removed!
>>>>
>>>> However maybe this single patch could go in 18.02.
>>>> +Santosh +Jerin since it's mostly about Octeon.
>>> rte_mempool_xmem_size should return correct size if MEMPOOL_F_CAPA_BLK_ALIGNED_OBJECTS flag
>>> is set in 'mp->flags'. Thats why _ops_get_capabilities() called in _populate_default() but not
>>> at _populate_iova().
>>> I think, this 'alone' patch may break octeontx mempool.
>> The patch does not touch rte_mempool_populate_default().
>> _ops_get_capabilities() is still called there before
>> rte_mempool_xmem_size(). The theoretical problem which
>> the patch tries to fix is the case when
>> rte_mempool_populate_default() is not called at all. I.e. application
>> calls _ops_get_capabilities() to get flags, then, together with
>> mp->flags, calls rte_mempool_xmem_size() directly, allocates
>> calculated amount of memory and calls _populate_iova().
>>
> In that case, Application does like below:
>
> 	/* Get mempool capabilities */
> 	mp_flags = 0;
> 	ret = rte_mempool_ops_get_capabilities(mp, &mp_flags);
> 	if ((ret < 0) && (ret != -ENOTSUP))
> 		return ret;
>
> 	/* update mempool capabilities */
> 	mp->flags |= mp_flags;

Above line is not mandatory. "mp->flags | mp_flags" could be simply
passed to  rte_mempool_xmem_size() below.

> 	/* calc xmem sz */
> 	size = rte_mempool_xmem_size(n, total_elt_sz, pg_shift,
> 					mp->flags);
>
> 	/* rsrv memory */
> 	mz = rte_memzone_reserve_aligned(mz_name, size,...);
>
> 	/* now populate iova */
> 	ret = rte_mempool_populate_iova(mp,,..);
>
> won't it work?
>
> However I understand that clubbing `_get_ops_capa() + flag-updation` into _populate_iova()
> perhaps better from user PoV.
>
>> Since later patches of the series reconsider memory size
>> calculation etc, it is up to you if it makes sense to apply it
>> in 18.02 as a fix.