Re: cansend app will block while it is sending RTR frames

[Marc Kleine-Budde <mkl@pengutronix.de>]

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On 08/28/2013 11:34 AM, xuewentian wrote:
> Hi all,
> 
>   I want to test sending a lot of RTR frames, because select/poll is no 
> effect on the flow control, I add the usleep in the cansend app.
>   
>   The code segment is :
>   
> 
> 	while (infinite || loopcount--) {
> 		
> 		ret = write(s, &frame, sizeof(frame));
> 		if (ret == -1) {
> 			perror("write");
> 			printf("Please specify a more long delay time!\n");
> 			break;
> 		}
> 		usleep(delay);//flow control
> 	}
> 
>   Here the "delay" is about 200us, and I used "cansend can0 -r -e -l 500 -
> i 0x1234567  0x11 0x22 0x33 0x44 0x55 0x66 0x77 0x88" command to send 500 
> RTR frames.but candump on
> the another board could only received the 336 frames,and candump app 
> hasn't print the received RTR frames,and only count the received frmaes.
>   and I debugged the send process in the kernel, and I found that it sleep 
> on the copy_from_user in the memcpy_fromiovec of the raw_sendmsg
>   
>   err = memcpy_fromiovec(skb_put(skb, size), msg->msg_iov, size);  // in 
> the raw_sendmsg function of the net/can/raw.c file.
> 	if (err < 0)
> 		goto free_skb;

How have you measured that the kernel sleeps in that function? How long
does it sleep?

>   What about happens with the write of the cansend app? and I used the 
> same way to send the 5000000 data frames, it didn't blocked.

Marc

-- 
Pengutronix e.K.                  | Marc Kleine-Budde           |
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