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Message-ID: <Ye/EQgqCBogZR87T@ip-172-31-19-208.ap-northeast-1.compute.internal> Date: Tue, 25 Jan 2022 09:34:58 +0000 From: Hyeonggon Yoo <42.hyeyoo@...il.com> To: Shay Agroskin <shayagr@...zon.com> Cc: Julian Wiedmann <jwiedmann.dev@...il.com>, netdev@...r.kernel.org, Arthur Kiyanovski <akiyano@...zon.com>, David Arinzon <darinzon@...zon.com>, Noam Dagan <ndagan@...zon.com>, Saeed Bishara <saeedb@...zon.com>, "David S . Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, Sameeh Jubran <sameehj@...zon.com>, Wei Yongjun <weiyongjun1@...wei.com>, Lorenzo Bianconi <lorenzo@...nel.org>, linux-kernel@...r.kernel.org Subject: Re: [PATCH] net: ena: Do not waste napi skb cache On Mon, Jan 24, 2022 at 10:50:05PM +0200, Shay Agroskin wrote: > > Julian Wiedmann <jwiedmann.dev@...il.com> writes: > > > On 24.01.22 10:57, Julian Wiedmann wrote: > > > On 23.01.22 13:56, Hyeonggon Yoo wrote: > > > > By profiling, discovered that ena device driver allocates skb by > > > > build_skb() and frees by napi_skb_cache_put(). Because the > > > > driver > > > > does not use napi skb cache in allocation path, napi skb cache > > > > is > > > > periodically filled and flushed. This is waste of napi skb > > > > cache. > > > > > > > > As ena_alloc_skb() is called only in napi, Use napi_build_skb() > > > > instead of build_skb() to when allocating skb. > > > > > > > > This patch was tested on aws a1.metal instance. > > > > > > > > Signed-off-by: Hyeonggon Yoo <42.hyeyoo@...il.com> > > > > --- > > > > drivers/net/ethernet/amazon/ena/ena_netdev.c | 2 +- > > > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > > > > > diff --git a/drivers/net/ethernet/amazon/ena/ena_netdev.c > > > > b/drivers/net/ethernet/amazon/ena/ena_netdev.c > > > > index c72f0c7ff4aa..2c67fb1703c5 100644 > > > > --- a/drivers/net/ethernet/amazon/ena/ena_netdev.c > > > > +++ b/drivers/net/ethernet/amazon/ena/ena_netdev.c > > > > @@ -1407,7 +1407,7 @@ static struct sk_buff > > > > *ena_alloc_skb(struct ena_ring *rx_ring, void *first_frag) > > > > skb = netdev_alloc_skb_ip_align(rx_ring->netdev, > > > > rx_ring->rx_copybreak); > > > > > > To keep things consistent, this should then also be > > > napi_alloc_skb(). > > > Right. I missed this. Thank you for pointing this! > > > > And on closer look, this copybreak path also looks buggy. If > > rx_copybreak > > gets reduced _while_ receiving a frame, the allocated skb can end up too > > small to take all the data. > > > > @ ena maintainers: can you please fix this? > > > Shay and Julian, Thank you for reviewing this. > Updating the copybreak value is done through ena_ethtool.c > (ena_set_tunable()) which updates `adapter->rx_copybreak`. > The adapter->rx_copybreak value is "propagated back" to the ring local > attributes (rx_ring->rx_copybreak) only after an interface toggle which > stops the napi routine first. > > Unless I'm missing something here I don't think the bug you're describing > exists. > > I agree that the netdev_alloc_skb_ip_align() can become napi_alloc_skb(). > Hyeonggon Yoo, can you please apply this change as well to this patch? > Okay. I'll update and test it again. BTW, It seems netdev_alloc_skb_ip_align() is used to make some fields be aligned. It's okay to just ignore this? Thanks, Hyeonggon. > Thanks, > Shay > > > > > > else > > > > - skb = build_skb(first_frag, ENA_PAGE_SIZE); > > > > + skb = napi_build_skb(first_frag, ENA_PAGE_SIZE); > > > > if (unlikely(!skb)) { > > > > ena_increase_stat(&rx_ring->rx_stats.skb_alloc_fail, 1, > > >
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