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

[Ilias Apalodimas]

On Tue, Dec 24, 2019 at 03:37:49PM +0100, Matteo Croce wrote:
> 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,
> 
> 
Jesper is rightm you aren't recycling anything.

The mark skb_mark_for_recycle() usage seems correct. 
There are a few more places that we refuse to recycle (for example coalescing
page pool and slub allocated pages is forbidden). I wonder if you hit any of
those cases and recycling doesn't take place. 
We'll hopefully release updated code shortly. I'll ping you and we can test on
that


Thanks
/Ilias
> 
> 
> --
> Matteo Croce
> per aspera ad upstream
>