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Date:   Wed, 21 Dec 2022 08:30:55 +0100
From:   Greg KH <greg@kroah.com>
To:     Leesoo Ahn <lsahn@ooseel.net>
Cc:     Oliver Neukum <oneukum@suse.com>,
        "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>, netdev@vger.kernel.org,
        linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] usbnet: optimize usbnet_bh() to reduce CPU load
Message-ID: <Y6K2L+t5NjK/3ipj@kroah.com>
References: <20221221044230.1012787-1-lsahn@ooseel.net>
 <Y6KoglOyuFEqfp2k@kroah.com>
 <2d4033ea-3034-24cf-493c-f60258f9988d@ooseel.net>
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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