Re: [PATCH v2] usbnet: optimize usbnet_bh() to reduce CPU load

[Leesoo Ahn]

On 22. 12. 21. 16:30, Greg KH wrote:
> On Wed, Dec 21, 2022 at 04:19:45PM +0900, Leesoo Ahn wrote:
> > On 22. 12. 21. 15:32, Greg KH wrote:
> > > On Wed, Dec 21, 2022 at 01:42:30PM +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>
> > > > ---
> > > > 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/
> > > > ---
> > > >    drivers/net/usb/usbnet.c | 19 +++++++++----------
> > > >    1 file changed, 9 insertions(+), 10 deletions(-)
> > > >
> > > > diff --git a/drivers/net/usb/usbnet.c b/drivers/net/usb/usbnet.c
> > > > index 64a9a80b2309..6e82fef90dd9 100644
> > > > --- a/drivers/net/usb/usbnet.c
> > > > +++ b/drivers/net/usb/usbnet.c
> > > > @@ -555,32 +555,30 @@ static int rx_submit (struct usbnet *dev, struct urb *urb, gfp_t flags)
> > > >    /*-------------------------------------------------------------------------*/
> > > > -static inline void rx_process (struct usbnet *dev, struct sk_buff *skb)
> > > > +static inline int rx_process(struct usbnet *dev, struct sk_buff *skb)
> > > >    {
> > > >    	if (dev->driver_info->rx_fixup &&
> > > >    	    !dev->driver_info->rx_fixup (dev, skb)) {
> > > >    		/* With RX_ASSEMBLE, rx_fixup() must update counters */
> > > >    		if (!(dev->driver_info->flags & FLAG_RX_ASSEMBLE))
> > > >    			dev->net->stats.rx_errors++;
> > > > -		goto done;
> > > > +		return 1;
> > > "1" means that you processed 1 byte, not that this is an error, which is
> > > what you want to say here, right?
> > No not at all..
> > > Please return a negative error value
> > > like I asked this to be changed to last time :(
> > Could you help me to decide the message type at this point please? I am
> > confused.
> I do not know, pick something that seems correct and we can go from
> there.  The important thing is that it is a -ERR value, not a positive
> one as that makes no sense for kernel functions.

Thank you for reviewing, v3 will be sent soon.

Best regards,
Leesoo