lkml.org 
[lkml]   [2022]   [Jan]   [24]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
SubjectRe: [PATCH] net: ena: Do not waste napi skb cache
Date

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,
>>

\
 
 \ /
  Last update: 2022-01-24 23:09    [W:0.054 / U:0.684 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site