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SubjectRe: [RFC net-next 0/2] mvpp2: page_pool support
On Tue, 24 Dec 2019 11:52:29 +0200
Ilias Apalodimas <ilias.apalodimas@linaro.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

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