Re: [dpdk-dev] ***Spam*** [PATCH 5/5] mempool: prevent objects from being across pages

[Olivier Matz <olivier.matz@6wind.com>]

On Tue, Oct 29, 2019 at 01:59:00PM +0300, Andrew Rybchenko wrote:
> On 10/28/19 5:01 PM, Olivier Matz wrote:
> > When populating a mempool, ensure that objects are not located across
> > several pages, except if user did not request iova contiguous objects.
> 
> I think it breaks distribution across memory channels which could
> affect performance significantly.

With 2M hugepages, there are ~900 mbufs per page, and all of them will
be distributed across memory channels. For larger objects, I don't think
the distribution is that important.

With small pages, that may be true. I think the problem was already
there except in IOVA=VA mode.

This should be fixable, but I'm not sure a use-case where we can see a
regression really exists.


> > Signed-off-by: Vamsi Krishna Attunuru <vattunuru@marvell.com>
> > Signed-off-by: Olivier Matz <olivier.matz@6wind.com>
> > ---
> >   lib/librte_mempool/rte_mempool.c             | 23 +++++-----------
> >   lib/librte_mempool/rte_mempool_ops_default.c | 29 ++++++++++++++++++--
> >   2 files changed, 33 insertions(+), 19 deletions(-)
> > 
> > diff --git a/lib/librte_mempool/rte_mempool.c b/lib/librte_mempool/rte_mempool.c
> > index 7664764e5..b23fd1b06 100644
> > --- a/lib/librte_mempool/rte_mempool.c
> > +++ b/lib/librte_mempool/rte_mempool.c
> > @@ -428,8 +428,6 @@ rte_mempool_get_page_size(struct rte_mempool *mp, size_t *pg_sz)
> >   	if (!need_iova_contig_obj)
> >   		*pg_sz = 0;
> > -	else if (!alloc_in_ext_mem && rte_eal_iova_mode() == RTE_IOVA_VA)
> > -		*pg_sz = 0;
> >   	else if (rte_eal_has_hugepages() || alloc_in_ext_mem)
> >   		*pg_sz = get_min_page_size(mp->socket_id);
> >   	else
> > @@ -478,17 +476,15 @@ rte_mempool_populate_default(struct rte_mempool *mp)
> >   	 * then just set page shift and page size to 0, because the user has
> >   	 * indicated that there's no need to care about anything.
> >   	 *
> > -	 * if we do need contiguous objects, there is also an option to reserve
> > -	 * the entire mempool memory as one contiguous block of memory, in
> > -	 * which case the page shift and alignment wouldn't matter as well.
> > +	 * if we do need contiguous objects (if a mempool driver has its
> > +	 * own calc_size() method returning min_chunk_size = mem_size),
> > +	 * there is also an option to reserve the entire mempool memory
> > +	 * as one contiguous block of memory.
> >   	 *
> >   	 * if we require contiguous objects, but not necessarily the entire
> > -	 * mempool reserved space to be contiguous, then there are two options.
> > -	 *
> > -	 * if our IO addresses are virtual, not actual physical (IOVA as VA
> > -	 * case), then no page shift needed - our memory allocation will give us
> > -	 * contiguous IO memory as far as the hardware is concerned, so
> > -	 * act as if we're getting contiguous memory.
> > +	 * mempool reserved space to be contiguous, pg_sz will be != 0,
> > +	 * and the default ops->populate() will take care of not placing
> > +	 * objects across pages.
> >   	 *
> >   	 * if our IO addresses are physical, we may get memory from bigger
> >   	 * pages, or we might get memory from smaller pages, and how much of it
> > @@ -501,11 +497,6 @@ rte_mempool_populate_default(struct rte_mempool *mp)
> >   	 *
> >   	 * If we fail to get enough contiguous memory, then we'll go and
> >   	 * reserve space in smaller chunks.
> > -	 *
> > -	 * We also have to take into account the fact that memory that we're
> > -	 * going to allocate from can belong to an externally allocated memory
> > -	 * area, in which case the assumption of IOVA as VA mode being
> > -	 * synonymous with IOVA contiguousness will not hold.
> >   	 */
> >   	need_iova_contig_obj = !(mp->flags & MEMPOOL_F_NO_IOVA_CONTIG);
> > diff --git a/lib/librte_mempool/rte_mempool_ops_default.c b/lib/librte_mempool/rte_mempool_ops_default.c
> > index f6aea7662..dd09a0a32 100644
> > --- a/lib/librte_mempool/rte_mempool_ops_default.c
> > +++ b/lib/librte_mempool/rte_mempool_ops_default.c
> > @@ -61,21 +61,44 @@ rte_mempool_op_calc_mem_size_default(const struct rte_mempool *mp,
> >   	return mem_size;
> >   }
> > +/* Returns -1 if object crosses a page boundary, else returns 0 */
> > +static int
> > +check_obj_bounds(char *obj, size_t pg_sz, size_t elt_sz)
> > +{
> > +	if (pg_sz == 0)
> > +		return 0;
> > +	if (elt_sz > pg_sz)
> > +		return 0;
> > +	if (RTE_PTR_ALIGN(obj, pg_sz) != RTE_PTR_ALIGN(obj + elt_sz - 1, pg_sz))
> > +		return -1;
> > +	return 0;
> > +}
> > +
> >   int
> >   rte_mempool_op_populate_default(struct rte_mempool *mp, unsigned int max_objs,
> >   		void *vaddr, rte_iova_t iova, size_t len,
> >   		rte_mempool_populate_obj_cb_t *obj_cb, void *obj_cb_arg)
> >   {
> > -	size_t total_elt_sz;
> > +	char *va = vaddr;
> > +	size_t total_elt_sz, pg_sz;
> >   	size_t off;
> >   	unsigned int i;
> >   	void *obj;
> > +	rte_mempool_get_page_size(mp, &pg_sz);
> > +
> 
> The function may return an error which should be taken into account here.

That would be better, indeed.


> >   	total_elt_sz = mp->header_size + mp->elt_size + mp->trailer_size;
> > -	for (off = 0, i = 0; off + total_elt_sz <= len && i < max_objs; i++) {
> > +	for (off = 0, i = 0; i < max_objs; i++) {
> > +		/* align offset to next page start if required */
> > +		if (check_obj_bounds(va + off, pg_sz, total_elt_sz) < 0)
> > +			off += RTE_PTR_ALIGN_CEIL(va + off, pg_sz) - (va + off);
> > +
> > +		if (off + total_elt_sz > len)
> > +			break;
> > +
> >   		off += mp->header_size;
> > -		obj = (char *)vaddr + off;
> > +		obj = va + off;
> >   		obj_cb(mp, obj_cb_arg, obj,
> >   		       (iova == RTE_BAD_IOVA) ? RTE_BAD_IOVA : (iova + off));
> >   		rte_mempool_ops_enqueue_bulk(mp, &obj, 1);
> 

Thanks for all the comments!
I will send a v2 tomorrow.

Olivier