Messages in this thread | | | From | Shay Agroskin <> | Subject | Re: [PATCH] net: ena: Do not waste napi skb cache | Date | Mon, 24 Jan 2022 22:50:05 +0200 |
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Julian Wiedmann <jwiedmann.dev@gmail.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@gmail.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(). >> > > 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? >
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?
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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