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

[santosh]

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 at dpdk.org
>>>>
>>>> Signed-off-by: Andrew Rybchenko <arybchenko at 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;

	/* 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.
>