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SubjectRe: [PATCH v2] usbnet: optimize usbnet_bh() to reduce CPU load
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@ooseel.net>
> > > ---
> > > 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/
> > > ---
> > > 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.

thanks,

greg k-h

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