netdev - Re: [RFC net-next 0/2] mvpp2: page

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Date:   Tue, 24 Dec 2019 15:00:58 +0100
From:   Jesper Dangaard Brouer <brouer@...hat.com>
To:     Ilias Apalodimas <ilias.apalodimas@...aro.org>
Cc:     Matteo Croce <mcroce@...hat.com>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Lorenzo Bianconi <lorenzo@...nel.org>,
        Maxime Chevallier <maxime.chevallier@...tlin.com>,
        Antoine Tenart <antoine.tenart@...tlin.com>,
        Luka Perkov <luka.perkov@...tura.hr>,
        Tomislav Tomasic <tomislav.tomasic@...tura.hr>,
        Marcin Wojtas <mw@...ihalf.com>,
        Stefan Chulski <stefanc@...vell.com>,
        Nadav Haklai <nadavh@...vell.com>, brouer@...hat.com
Subject: Re: [RFC net-next 0/2] mvpp2: page_pool support

On Tue, 24 Dec 2019 11:52:29 +0200
Ilias Apalodimas <ilias.apalodimas@...aro.org> 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