lkml.org 
[lkml]   [2022]   [Dec]   [19]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
SubjectRe: [PATCH] usbnet: jump to rx_cleanup case instead of calling skb_queue_tail
From

On 22. 12. 18. 17:55, Greg KH wrote:
> On Sun, Dec 18, 2022 at 01:18:51AM +0900, Leesoo Ahn wrote:
>> The current source pushes skb into dev->done queue by calling
>> skb_queue_tail() and then, call skb_dequeue() to pop for rx_cleanup state
>> to free urb and skb next in usbnet_bh().
>> It wastes CPU resource with extra instructions. Instead, use return values
>> jumping to rx_cleanup case directly to free them. Therefore calling
>> skb_queue_tail() and skb_dequeue() is not necessary.
>>
>> The follows are just showing difference between calling skb_queue_tail()
>> and using return values jumping to rx_cleanup state directly in usbnet_bh()
>> in Arm64 instructions with perf tool.
>>
>> ----------- calling skb_queue_tail() -----------
>> │ if (!(dev->driver_info->flags & FLAG_RX_ASSEMBLE))
>> 7.58 │248: ldr x0, [x20, #16]
>> 2.46 │24c: ldr w0, [x0, #8]
>> 1.64 │250: ↑ tbnz w0, #14, 16c
>> │ dev->net->stats.rx_errors++;
>> 0.57 │254: ldr x1, [x20, #184]
>> 1.64 │258: ldr x0, [x1, #336]
>> 2.65 │25c: add x0, x0, #0x1
>> │260: str x0, [x1, #336]
>> │ skb_queue_tail(&dev->done, skb);
>> 0.38 │264: mov x1, x19
>> │268: mov x0, x21
>> 2.27 │26c: → bl skb_queue_tail
>> 0.57 │270: ↑ b 44 // branch to call skb_dequeue()
>>
>> ----------- jumping to rx_cleanup state -----------
>> │ if (!(dev->driver_info->flags & FLAG_RX_ASSEMBLE))
>> 1.69 │25c: ldr x0, [x21, #16]
>> 4.78 │260: ldr w0, [x0, #8]
>> 3.28 │264: ↑ tbnz w0, #14, e4 // jump to 'rx_cleanup' state
>> │ dev->net->stats.rx_errors++;
>> 0.09 │268: ldr x1, [x21, #184]
>> 2.72 │26c: ldr x0, [x1, #336]
>> 3.37 │270: add x0, x0, #0x1
>> 0.09 │274: str x0, [x1, #336]
>> 0.66 │278: ↑ b e4 // branch to 'rx_cleanup' state
> Interesting, but does this even really matter given the slow speed of
> the USB hardware?

It doesn't if USB hardware has slow speed but in software view, it's
still worth avoiding calling skb_queue_tail() and skb_dequeue() which
work with spinlock, if possible.


>> Signed-off-by: Leesoo Ahn <lsahn@ooseel.net>
>> ---
>> drivers/net/usb/usbnet.c | 11 ++++++-----
>> 1 file changed, 6 insertions(+), 5 deletions(-)
>>
>> diff --git a/drivers/net/usb/usbnet.c b/drivers/net/usb/usbnet.c
>> index 64a9a80b2309..924392a37297 100644
>> --- a/drivers/net/usb/usbnet.c
>> +++ b/drivers/net/usb/usbnet.c
>> @@ -555,7 +555,7 @@ 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)) {
>> @@ -576,11 +576,11 @@ static inline void rx_process (struct usbnet *dev, struct sk_buff *skb)
>> netif_dbg(dev, rx_err, dev->net, "rx length %d\n", skb->len);
>> } else {
>> usbnet_skb_return(dev, skb);
>> - return;
>> + return 0;
>> }
>>
>> done:
>> - skb_queue_tail(&dev->done, skb);
>> + return -1;
> Don't make up error numbers, this makes it look like this failed, not
> succeeded. And if this failed, give it a real error value.
>
> thanks,
>
> greg k-h

Best regards,
Leesoo

\
 
 \ /
  Last update: 2022-12-19 08:42    [W:0.068 / U:0.220 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site