netdev - Re: [PATCH v3] usbnet: optimize usbnet

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Date:   Mon, 26 Dec 2022 15:24:57 +0900
From:   Leesoo Ahn <lsahn@...eel.net>
To:     Paolo Abeni <pabeni@...hat.com>
Cc:     Oliver Neukum <oneukum@...e.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>, Greg KH <greg@...ah.com>,
        netdev@...r.kernel.org, linux-usb@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] usbnet: optimize usbnet_bh() to reduce CPU load



22. 12. 22. 20:13에 Paolo Abeni 이(가) 쓴 글:
> On Wed, 2022-12-21 at 16:59 +0900, Leesoo Ahn wrote:
>> The current source pushes skb into dev->done queue by calling
>> skb_queue_tail() and then pop it by calling skb_dequeue() to branch to
>> rx_cleanup state for freeing urb/skb in usbnet_bh(). It takes extra CPU
>> load, 2.21% (skb_queue_tail) as follows.
>>
>> -   11.58%     0.26%  swapper          [k] usbnet_bh
>>     - 11.32% usbnet_bh
>>        - 6.43% skb_dequeue
>>             6.34% _raw_spin_unlock_irqrestore
>>        - 2.21% skb_queue_tail
>>             2.19% _raw_spin_unlock_irqrestore
>>        - 1.68% consume_skb
>>           - 0.97% kfree_skbmem
>>                0.80% kmem_cache_free
>>             0.53% skb_release_data
>>
>> To reduce the extra CPU load use return values jumping to rx_cleanup
>> state directly to free them instead of calling skb_queue_tail() and
>> skb_dequeue() for push/pop respectively.
>>
>> -    7.87%     0.25%  swapper          [k] usbnet_bh
>>     - 7.62% usbnet_bh
>>        - 4.81% skb_dequeue
>>             4.74% _raw_spin_unlock_irqrestore
>>        - 1.75% consume_skb
>>           - 0.98% kfree_skbmem
>>                0.78% kmem_cache_free
>>             0.58% skb_release_data
>>          0.53% smsc95xx_rx_fixup
>>
>> Signed-off-by: Leesoo Ahn <lsahn@...eel.net>
>> ---
>> v3:
>>    - Replace return values with proper -ERR values in rx_process()
>>
>> v2:
>>    - Replace goto label with return statement to reduce goto entropy
>>    - Add CPU load information by perf in commit message
>>
>> v1 at:
>>    https://patchwork.kernel.org/project/netdevbpf/patch/20221217161851.829497-1-lsahn@ooseel.net/
> 
> This looks like net-next material.
> 
> We have already submitted the networking pull request to Linus
> for v6.2 and therefore net-next is closed for new drivers, features,
> code refactoring and optimizations. We are currently accepting
> bug fixes only.
> 
> Please repost when net-next reopens after Jan 2nd, including the
> expected 'net-next' tag into the subject line
> 
> RFC patches sent for review only are obviously welcome at any time.
> 
> [...]
> 
>> @@ -1528,13 +1526,14 @@ static void usbnet_bh (struct timer_list *t)
>>   		entry = (struct skb_data *) skb->cb;
>>   		switch (entry->state) {
>>   		case rx_done:
>> -			entry->state = rx_cleanup;
>> -			rx_process (dev, skb);
>> +			if (rx_process(dev, skb))
>> +				goto cleanup;
> 
> You can avoid this additional label (which is a little confusing inside
> a switch) factoring out a usb_free_skb(skb) helper and calling it here
> and under the rx_cleanup case.

Thank you for the information and feedback, it will be in v4 when 
net-next reopens.

Best regards,
Leesoo