From: Ilias Apalodimas <ilias.apalodimas@linaro.org>
To: Jesper Dangaard Brouer <brouer@redhat.com>
Cc: Jose Abreu <Jose.Abreu@synopsys.com>,
Joao Pinto <Joao.Pinto@synopsys.com>,
Alexandre Torgue <alexandre.torgue@st.com>,
Maxime Ripard <maxime.ripard@bootlin.com>,
netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
"David S . Miller" <davem@davemloft.net>,
Chen-Yu Tsai <wens@csie.org>,
Maxime Coquelin <mcoquelin.stm32@gmail.com>,
Giuseppe Cavallaro <peppe.cavallaro@st.com>,
linux-stm32@st-md-mailman.stormreply.com,
linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH net-next 3/3] net: stmmac: Introducing support for Page Pool
Date: Thu, 4 Jul 2019 13:30:57 +0300 [thread overview]
Message-ID: <20190704103057.GA29734@apalos> (raw)
In-Reply-To: <20190704120018.4523a119@carbon>
HI Jesper, Ivan,
> On Wed, 3 Jul 2019 12:37:50 +0200
> Jose Abreu <Jose.Abreu@synopsys.com> wrote:
>
> > @@ -3547,6 +3456,9 @@ static int stmmac_rx(struct stmmac_priv *priv, int limit, u32 queue)
> >
> > napi_gro_receive(&ch->rx_napi, skb);
> >
> > + page_pool_recycle_direct(rx_q->page_pool, buf->page);
>
> This doesn't look correct.
>
> The page_pool DMA mapping cannot be "kept" when page traveling into the
> network stack attached to an SKB. (Ilias and I have a long term plan[1]
> to allow this, but you cannot do it ATM).
>
> You will have to call:
> page_pool_release_page(rx_q->page_pool, buf->page);
>
> This will do a DMA-unmap, and you will likely loose your performance
> gain :-(
>
>
> > + buf->page = NULL;
> > +
> > priv->dev->stats.rx_packets++;
> > priv->dev->stats.rx_bytes += frame_len;
> > }
>
> Also remember that the page_pool requires you driver to do the DMA-sync
> operation. I see a dma_sync_single_for_cpu(), but I didn't see a
> dma_sync_single_for_device() (well, I noticed one getting removed).
> (For some HW Ilias tells me that the dma_sync_single_for_device can be
> elided, so maybe this can still be correct for you).
On our case (and in the page_pool API in general) you have to track buffers when
both .ndo_xdp_xmit() and XDP_TX are used.
So the lifetime of a packet might be
1. page pool allocs packet. The API doesn't sync but i *think* you don't have to
explicitly since the CPU won't touch that buffer until the NAPI handler kicks
in. On the napi handler you need to dma_sync_single_for_cpu() and process the
packet.
2a) no XDP is required so the packet is unmapped and free'd
2b) .ndo_xdp_xmit is called so tyhe buffer need to be mapped/unmapped
2c) XDP_TX is called. In that case we re-use an Rx buffer so we need to
dma_sync_single_for_device()
2a and 2b won't cause any issues
In 2c the buffer will be recycled and fed back to the device with a *correct*
sync (for_device) and all those buffers are allocated as DMA_BIDIRECTIONAL.
So bvottom line i *think* we can skip the dma_sync_single_for_device() on the
initial allocation *only*. If am terribly wrong please let me know :)
Thanks
/Ilias
>
>
> [1] https://github.com/xdp-project/xdp-project/blob/master/areas/mem/page_pool02_SKB_return_callback.org
> --
> Best regards,
> Jesper Dangaard Brouer
> MSc.CS, Principal Kernel Engineer at Red Hat
> LinkedIn: http://www.linkedin.com/in/brouer
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next prev parent reply other threads:[~2019-07-04 10:31 UTC|newest]
Thread overview: 86+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-03 10:37 [PATCH net-next 0/3] net: stmmac: Some performance improvements and a fix Jose Abreu
2019-07-03 10:37 ` [PATCH net-next 1/3] net: stmmac: Implement RX Coalesce Frames setting Jose Abreu
2019-07-03 20:41 ` Jakub Kicinski
2019-07-03 10:37 ` [PATCH net-next 2/3] net: stmmac: Fix descriptors address being in > 32 bits address space Jose Abreu
2019-07-03 10:37 ` [PATCH net-next 3/3] net: stmmac: Introducing support for Page Pool Jose Abreu
2019-07-03 10:40 ` Jose Abreu
2019-07-04 9:39 ` Jesper Dangaard Brouer
2019-07-04 14:45 ` Jose Abreu
2019-07-04 15:09 ` Jesper Dangaard Brouer
2019-07-04 15:18 ` Jose Abreu
2019-07-04 15:33 ` Jesper Dangaard Brouer
2019-07-04 9:48 ` Jesper Dangaard Brouer
2019-07-04 10:00 ` Jesper Dangaard Brouer
2019-07-04 10:13 ` Jose Abreu
2019-07-04 11:11 ` Ilias Apalodimas
2019-07-04 11:54 ` Jesper Dangaard Brouer
2019-07-04 12:04 ` Ilias Apalodimas
2019-07-04 12:59 ` Jose Abreu
2019-07-04 13:06 ` Ilias Apalodimas
2019-07-04 10:30 ` Ilias Apalodimas [this message]
2019-07-04 12:14 ` Arnd Bergmann
2019-07-04 12:49 ` Ilias Apalodimas
2019-07-17 18:58 ` Jon Hunter
2019-07-18 7:29 ` Jose Abreu
2019-07-18 7:48 ` Jose Abreu
2019-07-18 9:16 ` Jon Hunter
2019-07-19 7:51 ` Jose Abreu
2019-07-19 8:37 ` Jon Hunter
2019-07-19 8:44 ` Jose Abreu
2019-07-19 8:49 ` Jon Hunter
2019-07-19 10:25 ` Jose Abreu
2019-07-19 12:28 ` Jose Abreu
2019-07-19 13:33 ` Jon Hunter
2019-07-19 12:30 ` Jon Hunter
2019-07-19 12:32 ` Jose Abreu
[not found] ` <25512348-5b98-aeb7-a6fb-f90376e66a84@nvidia.com>
2019-07-22 7:23 ` Jose Abreu
2019-07-22 9:37 ` Jon Hunter
2019-07-22 9:47 ` Jose Abreu
2019-07-22 9:57 ` Jose Abreu
2019-07-22 10:27 ` Jon Hunter
2019-07-22 10:18 ` Ilias Apalodimas
2019-07-22 11:11 ` Lars Persson
2019-07-22 11:39 ` Jose Abreu
2019-07-22 12:05 ` Jon Hunter
2019-07-22 14:04 ` Jose Abreu
2019-07-23 8:14 ` Jose Abreu
2019-07-23 10:01 ` Jon Hunter
2019-07-23 10:07 ` Jose Abreu
2019-07-23 10:29 ` Robin Murphy
2019-07-23 11:22 ` Jose Abreu
2019-07-23 12:09 ` Jon Hunter
2019-07-23 13:19 ` Robin Murphy
2019-07-23 21:39 ` Jon Hunter
2019-07-24 10:03 ` Robin Murphy
2019-07-23 18:51 ` David Miller
2019-07-24 8:54 ` Ilias Apalodimas
2019-07-24 9:43 ` Jose Abreu
2019-07-24 9:53 ` Ilias Apalodimas
2019-07-24 10:04 ` Jose Abreu
2019-07-24 11:10 ` Jon Hunter
2019-07-24 11:34 ` Jose Abreu
2019-07-24 11:58 ` Jon Hunter
2019-07-25 7:44 ` Jose Abreu
2019-07-25 9:45 ` Jon Hunter
2019-07-25 11:39 ` Ilias Apalodimas
2019-07-23 10:38 ` Jon Hunter
2019-07-23 10:49 ` Jose Abreu
2019-07-23 11:58 ` Jon Hunter
2019-07-23 12:51 ` Jose Abreu
2019-07-23 13:34 ` Jon Hunter
2019-07-29 9:45 ` Mikko Perttunen
2019-07-25 13:20 ` Jon Hunter
2019-07-25 13:26 ` Jose Abreu
2019-07-25 14:25 ` Jon Hunter
2019-07-25 15:12 ` Jose Abreu
2019-07-26 14:11 ` Jon Hunter
2019-07-27 15:56 ` Jose Abreu
2019-07-29 8:16 ` Jose Abreu
2019-07-29 10:55 ` Jon Hunter
2019-07-29 11:29 ` Jose Abreu
2019-07-29 11:52 ` Robin Murphy
2019-07-29 14:08 ` Jose Abreu
2019-07-29 21:33 ` Jon Hunter
2019-07-30 9:39 ` Jose Abreu
2019-07-30 13:36 ` Jon Hunter
2019-07-30 13:58 ` Jose Abreu
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