Re: [PATCH v3] usbnet: optimize usbnet_bh() to reduce CPU load

[Leesoo Ahn]

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@xxxxxxxxxx>
> > ---
> > 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@xxxxxxxxxx/
>
> 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