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Date: Wed, 21 Dec 2022 16:19:45 +0900 From: Leesoo Ahn <lsahn@...eel.net> To: Greg KH <greg@...ah.com> Cc: Oliver Neukum <oneukum@...e.com>, "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org, linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org Subject: Re: [PATCH v2] usbnet: optimize usbnet_bh() to reduce CPU load 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@...eel.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. The return value totally depends on how rx_fixup() is. For instance, in smsc95xx.c, smsc95xx_rx_fixup() function returns 0 in two cases that 1) frame size is greater than ETH_FRAME_LEN(1526 bytes) as follows 1853 /* ETH_FRAME_LEN + 4(CRC) + 2(COE) + 4(Vlan) */ 1854 if (unlikely(size > (ETH_FRAME_LEN + 12))) { 1855 netif_dbg(dev, rx_err, dev->net, 1856 "size err header=0x%08x\n", header); 1857 return 0; 1858 } 2) it is failed for skb allocation, but memory? 1870 ax_skb = skb_clone(skb, GFP_ATOMIC); 1871 if (unlikely(!ax_skb)) { 1872 netdev_warn(dev->net, "Error allocating skb\n"); 1873 return 0; 1874 } I guess EPROTO or ENOMEM, one of them could be the value at the point but I have no ideas.. Best regards, Leesoo
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