From: Ilias Apalodimas <ilias.apalodimas@linaro.org>
To: Alexander Lobakin <alobakin@pm.me>
Cc: Matteo Croce <mcroce@linux.microsoft.com>,
Jesper Dangaard Brouer <jbrouer@redhat.com>,
netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
Jonathan Lemon <jonathan.lemon@gmail.com>,
"David S. Miller" <davem@davemloft.net>,
Jesper Dangaard Brouer <hawk@kernel.org>,
Lorenzo Bianconi <lorenzo@kernel.org>,
Saeed Mahameed <saeedm@nvidia.com>,
David Ahern <dsahern@gmail.com>,
Saeed Mahameed <saeed@kernel.org>, Andrew Lunn <andrew@lunn.ch>
Subject: Re: [PATCH net-next 0/6] page_pool: recycle buffers
Date: Tue, 23 Mar 2021 19:01:52 +0200 [thread overview]
Message-ID: <YFofANKiR3tD9zgm@enceladus> (raw)
In-Reply-To: <20210323165523.187134-1-alobakin@pm.me>
On Tue, Mar 23, 2021 at 04:55:31PM +0000, Alexander Lobakin wrote:
> > > > > >
[...]
> > > > >
> > > > > 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)
>
> Sure, I'll drop perf tools to my test env and share the results,
> maybe tomorrow or in a few days.
> From what I know for sure about MIPS and my platform,
> post-Rx synching (dma_sync_single_for_cpu()) is a no-op, and
> pre-Rx (dma_sync_single_for_device() etc.) is a bit expensive.
> I always have sane page_pool->pp.max_len value (smth about 1668
> for MTU of 1500) to minimize the overhead.
>
> By the word, IIRC, all machines shipped with mvpp2 have hardware
> cache coherency units and don't suffer from sync routines at all.
> That may be the reason why mvpp2 wins the most from this series.
Yep exactly. It's also the reason why you explicitly have to opt-in using the
recycling (by marking the skb for it), instead of hiding the feature in the
page pool internals
Cheers
/Ilias
>
> > > > > >
> > > > > > [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.
>
> mvpp2 driver doesn't use napi_consume_skb() on its Tx completion path.
> As a result, NAPI percpu caches get refilled only through
> kmem_cache_alloc_bulk(), and most of skbuff_head recycling
> doesn't work.
>
> > Regards,
> > --
> > per aspera ad upstream
>
> Oh, I love that one!
>
> Al
>
next prev parent reply other threads:[~2021-03-23 17:02 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-22 17:02 [PATCH net-next 0/6] page_pool: recycle buffers Matteo Croce
2021-03-22 17:02 ` [PATCH net-next 1/6] xdp: reduce size of struct xdp_mem_info Matteo Croce
2021-03-22 17:02 ` [PATCH net-next 2/6] mm: add a signature in struct page Matteo Croce
2021-03-22 17:02 ` [PATCH net-next 3/6] page_pool: DMA handling and allow to recycles frames via SKB Matteo Croce
2021-03-22 19:38 ` Matteo Croce
2021-03-22 17:02 ` [PATCH net-next 4/6] net: change users of __skb_frag_unref() and add an extra argument Matteo Croce
2021-03-22 17:03 ` [PATCH net-next 5/6] mvpp2: recycle buffers Matteo Croce
2021-03-22 17:03 ` [PATCH net-next 6/6] mvneta: " Matteo Croce
2021-03-23 15:06 ` Jesper Dangaard Brouer
2021-03-24 9:28 ` Lorenzo Bianconi
2021-03-24 21:48 ` Ilias Apalodimas
2021-03-23 14:57 ` [PATCH net-next 0/6] page_pool: " David Ahern
2021-03-23 15:03 ` Ilias Apalodimas
2021-03-23 15:41 ` Alexander Lobakin
2021-03-23 15:47 ` Ilias Apalodimas
2021-03-23 16:04 ` Jesper Dangaard Brouer
2021-03-23 16:10 ` Ilias Apalodimas
2021-03-23 16:28 ` Matteo Croce
2021-03-23 16:55 ` Alexander Lobakin
2021-03-23 17:01 ` Ilias Apalodimas [this message]
2021-03-23 20:03 ` Alexander Lobakin
2021-03-24 7:50 ` Ilias Apalodimas
2021-03-24 11:42 ` Alexander Lobakin
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