Re: [RFC net-next 0/2] mvpp2: page_pool support

[Matteo Croce]

On Tue, Dec 24, 2019 at 3:01 PM Jesper Dangaard Brouer
<brouer@xxxxxxxxxx> wrote:
>
> On Tue, 24 Dec 2019 11:52:29 +0200
> Ilias Apalodimas <ilias.apalodimas@xxxxxxxxxx> wrote:
>
> > On Tue, Dec 24, 2019 at 02:01:01AM +0100, Matteo Croce wrote:
> > > This patches change the memory allocator of mvpp2 from the frag allocator to
> > > the page_pool API. This change is needed to add later XDP support to mvpp2.
> > >
> > > The reason I send it as RFC is that with this changeset, mvpp2 performs much
> > > more slower. This is the tc drop rate measured with a single flow:
> > >
> > > stock net-next with frag allocator:
> > > rx: 900.7 Mbps 1877 Kpps
> > >
> > > this patchset with page_pool:
> > > rx: 423.5 Mbps 882.3 Kpps
> > >
> > > This is the perf top when receiving traffic:
> > >
> > >   27.68%  [kernel]            [k] __page_pool_clean_page
> >
> > This seems extremly high on the list.
>
> This looks related to the cost of dma unmap, as page_pool have
> PP_FLAG_DMA_MAP. (It is a little strange, as page_pool have flag
> DMA_ATTR_SKIP_CPU_SYNC, which should make it less expensive).
>
>
> > >    9.79%  [kernel]            [k] get_page_from_freelist
>
> You are clearly hitting page-allocator every time, because you are not
> using page_pool recycle facility.
>
>
> > >    7.18%  [kernel]            [k] free_unref_page
> > >    4.64%  [kernel]            [k] build_skb
> > >    4.63%  [kernel]            [k] __netif_receive_skb_core
> > >    3.83%  [mvpp2]             [k] mvpp2_poll
> > >    3.64%  [kernel]            [k] eth_type_trans
> > >    3.61%  [kernel]            [k] kmem_cache_free
> > >    3.03%  [kernel]            [k] kmem_cache_alloc
> > >    2.76%  [kernel]            [k] dev_gro_receive
> > >    2.69%  [mvpp2]             [k] mvpp2_bm_pool_put
> > >    2.68%  [kernel]            [k] page_frag_free
> > >    1.83%  [kernel]            [k] inet_gro_receive
> > >    1.74%  [kernel]            [k] page_pool_alloc_pages
> > >    1.70%  [kernel]            [k] __build_skb
> > >    1.47%  [kernel]            [k] __alloc_pages_nodemask
> > >    1.36%  [mvpp2]             [k] mvpp2_buf_alloc.isra.0
> > >    1.29%  [kernel]            [k] tcf_action_exec
> > >
> > > I tried Ilias patches for page_pool recycling, I get an improvement
> > > to ~1100, but I'm still far than the original allocator.
> --
> Best regards,
>   Jesper Dangaard Brouer
>   MSc.CS, Principal Kernel Engineer at Red Hat
>   LinkedIn: http://www.linkedin.com/in/brouer
>

The change I did to use the recycling is the following:

--- a/drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c
+++ b/drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c
@@ -3071,7 +3071,7 @@ static int mvpp2_rx(struct mvpp2_port *port,
struct napi_struct *napi,
    if (pp)
-       page_pool_release_page(pp, virt_to_page(data));
+      skb_mark_for_recycle(skb, virt_to_page(data), &rxq->xdp_rxq.mem);
    else
         dma_unmap_single_attrs(dev->dev.parent, dma_addr,




--
Matteo Croce
per aspera ad upstream