[PATCH] net: ena: Do not waste napi skb cache

[PATCH] net: ena: Do not waste napi skb cache

[Hyeonggon Yoo]

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);
 	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,
-- 
2.33.1

Re: [PATCH] net: ena: Do not waste napi skb cache

[Julian Wiedmann]

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().

>  	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,

Re: [PATCH] net: ena: Do not waste napi skb cache

[Julian Wiedmann]

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?

>>  	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,
> 

Re: [PATCH] net: ena: Do not waste napi skb cache

[Shay Agroskin]

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,
>> 

Re: [PATCH] net: ena: Do not waste napi skb cache

[Hyeonggon Yoo]

On Mon, Jan 24, 2022 at 10:50:05PM +0200, Shay Agroskin wrote:
> 
> 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().
> > >

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,
> > > 

Re: [PATCH] net: ena: Do not waste napi skb cache

[Julian Wiedmann]

On 25.01.22 11:34, Hyeonggon Yoo wrote:
> On Mon, Jan 24, 2022 at 10:50:05PM +0200, Shay Agroskin wrote:
>>

[...]

>>
>> 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?
> 

napi_alloc_skb() adds NET_IP_ALIGN internally, so you end up with the same alignment as before.


> 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,
>>>>

Re: [PATCH] net: ena: Do not waste napi skb cache

[Hyeonggon Yoo]

On Tue, Jan 25, 2022 at 03:50:30PM +0200, Julian Wiedmann wrote:
> On 25.01.22 11:34, Hyeonggon Yoo wrote:
> > On Mon, Jan 24, 2022 at 10:50:05PM +0200, Shay Agroskin wrote:
> >>
> 
> [...]
> 
> >>
> >> 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?
> > 
> 
> napi_alloc_skb() adds NET_IP_ALIGN internally, so you end up with the same alignment as before.
> 

Oh I was missing that. I updated the patch and tested again.
Thank you!

> 
> > 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,
> >>>>
> 

Re: [PATCH] net: ena: Do not waste napi skb cache

[Julian Wiedmann]

On 24.01.22 22:50, Shay Agroskin wrote:
> 
> 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.
> 

That's unfortunate. ena_get_tunable() returns the updated adapter->rx_copybreak, how would a user know that their update isn't actually live yet?

> Unless I'm missing something here I don't think the bug you're describing exists.
> 

ack, thanks for double-checking!

> 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,
>>>