netdev - Re: [PATCH net-next 0/6] page

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Date:   Tue, 23 Mar 2021 17:28:32 +0100
From:   Matteo Croce <mcroce@...ux.microsoft.com>
To:     Ilias Apalodimas <ilias.apalodimas@...aro.org>
Cc:     Jesper Dangaard Brouer <jbrouer@...hat.com>,
        Alexander Lobakin <alobakin@...me>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Jonathan Lemon <jonathan.lemon@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        Lorenzo Bianconi <lorenzo@...nel.org>,
        Saeed Mahameed <saeedm@...dia.com>,
        David Ahern <dsahern@...il.com>,
        Saeed Mahameed <saeed@...nel.org>, Andrew Lunn <andrew@...n.ch>
Subject: Re: [PATCH net-next 0/6] page_pool: recycle buffers

On Tue, Mar 23, 2021 at 5:10 PM Ilias Apalodimas
<ilias.apalodimas@...aro.org> wrote:
>
> On Tue, Mar 23, 2021 at 05:04:47PM +0100, Jesper Dangaard Brouer wrote:
> > On Tue, 23 Mar 2021 17:47:46 +0200
> > Ilias Apalodimas <ilias.apalodimas@...aro.org> wrote:
> >
> > > On Tue, Mar 23, 2021 at 03:41:23PM +0000, Alexander Lobakin wrote:
> > > > From: Matteo Croce <mcroce@...ux.microsoft.com>
> > > > Date: Mon, 22 Mar 2021 18:02:55 +0100
> > > >
> > > > > From: Matteo Croce <mcroce@...rosoft.com>
> > > > >
> > > > > This series enables recycling of the buffers allocated with the page_pool API.
> > > > > The first two patches are just prerequisite to save space in a struct and
> > > > > avoid recycling pages allocated with other API.
> > > > > Patch 2 was based on a previous idea from Jonathan Lemon.
> > > > >
> > > > > The third one is the real recycling, 4 fixes the compilation of __skb_frag_unref
> > > > > users, and 5,6 enable the recycling on two drivers.
> > > > >
> > > > > In the last two patches I reported the improvement I have with the series.
> > > > >
> > > > > The recycling as is can't be used with drivers like mlx5 which do page split,
> > > > > but this is documented in a comment.
> > > > > In the future, a refcount can be used so to support mlx5 with no changes.
> > > > >
> > > > > Ilias Apalodimas (2):
> > > > >   page_pool: DMA handling and allow to recycles frames via SKB
> > > > >   net: change users of __skb_frag_unref() and add an extra argument
> > > > >
> > > > > Jesper Dangaard Brouer (1):
> > > > >   xdp: reduce size of struct xdp_mem_info
> > > > >
> > > > > Matteo Croce (3):
> > > > >   mm: add a signature in struct page
> > > > >   mvpp2: recycle buffers
> > > > >   mvneta: recycle buffers
> > > > >
> > > > >  .../chelsio/inline_crypto/ch_ktls/chcr_ktls.c |  2 +-
> > > > >  drivers/net/ethernet/marvell/mvneta.c         |  4 +-
> > > > >  .../net/ethernet/marvell/mvpp2/mvpp2_main.c   | 17 +++----
> > > > >  drivers/net/ethernet/marvell/sky2.c           |  2 +-
> > > > >  drivers/net/ethernet/mellanox/mlx4/en_rx.c    |  2 +-
> > > > >  include/linux/mm_types.h                      |  1 +
> > > > >  include/linux/skbuff.h                        | 33 +++++++++++--
> > > > >  include/net/page_pool.h                       | 15 ++++++
> > > > >  include/net/xdp.h                             |  5 +-
> > > > >  net/core/page_pool.c                          | 47 +++++++++++++++++++
> > > > >  net/core/skbuff.c                             | 20 +++++++-
> > > > >  net/core/xdp.c                                | 14 ++++--
> > > > >  net/tls/tls_device.c                          |  2 +-
> > > > >  13 files changed, 138 insertions(+), 26 deletions(-)
> > > >
> > > > Just for the reference, I've performed some tests on 1G SoC NIC with
> > > > this patchset on, here's direct link: [0]
> > > >
> > >
> > > Thanks for the testing!
> > > Any chance you can get a perf measurement on this?
> >
> > I guess you mean perf-report (--stdio) output, right?
> >
>
> Yea,
> As hinted below, I am just trying to figure out if on Alexander's platform the
> cost of syncing, is bigger that free-allocate. I remember one armv7 were that
> was the case.
>
> > > Is DMA syncing taking a substantial amount of your cpu usage?
> >
> > (+1 this is an important question)
> >
> > > >
> > > > [0] https://lore.kernel.org/netdev/20210323153550.130385-1-alobakin@pm.me
> > > >
> >

That would be the same as for mvneta:

Overhead  Shared Object     Symbol
  24.10%  [kernel]          [k] __pi___inval_dcache_area
  23.02%  [mvneta]          [k] mvneta_rx_swbm
   7.19%  [kernel]          [k] kmem_cache_alloc

Anyway, I tried to use the recycling *and* napi_build_skb on mvpp2,
and I get lower packet rate than recycling alone.
I don't know why, we should investigate it.

Regards,
-- 
per aspera ad upstream