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Commit b791072b authored by Will Schmidt's avatar Will Schmidt Committed by Paul Mackerras
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[POWERPC] hvc_console: Polling mode timer backoff 



Add a back-off mechanism to hvc_console's polling logic.   This change
drops the timers/second ratio from ~90 to ~1/2 while the console is
idle.
This change is most noticeable when watching /proc/timer_stats output.

This only affects when the hvc_console is running in poll mode, i.e.
power4 and cell systems.

I've tested on Power4, Michael Ellerman has both contributed to the
patch and tested on cell.

Signed-off-by: default avatarWill Schmidt <will_schmidt@vnet.ibm.com>
Signed-off-by: default avatarMichael Ellerman <michael@ellerman.id.au>
Acked-by: default avatarLinas Vepstas <linas@austin.ibm.com>
Signed-off-by: default avatarPaul Mackerras <paulus@samba.org>
parent b3a6d2a5

drivers/char/hvc_console.c

+25 −6
Original line number Diff line number Diff line
@@ -47,8 +47,6 @@ 
#define HVC_MAJOR	229

#define HVC_MINOR	0



#define TIMEOUT		(10)



/*

 * Wait this long per iteration while trying to push buffered data to the

 * hypervisor before allowing the tty to complete a close operation.
@@ -550,6 +548,18 @@ static int hvc_chars_in_buffer(struct tty_struct *tty) 
	return hp->n_outbuf;

}



/*

 * timeout will vary between the MIN and MAX values defined here.  By default

 * and during console activity we will use a default MIN_TIMEOUT of 10.  When

 * the console is idle, we increase the timeout value on each pass through

 * msleep until we reach the max.  This may be noticeable as a brief (average

 * one second) delay on the console before the console responds to input when

 * there has been no input for some time.

 */

#define MIN_TIMEOUT		(10)

#define MAX_TIMEOUT		(2000)

static u32 timeout = MIN_TIMEOUT;



#define HVC_POLL_READ	0x00000001

#define HVC_POLL_WRITE	0x00000002
@@ -642,8 +652,13 @@ static int hvc_poll(struct hvc_struct *hp) 
 bail:

	spin_unlock_irqrestore(&hp->lock, flags);



	if (read_total)

	if (read_total) {

		/* Activity is occurring, so reset the polling backoff value to

		   a minimum for performance. */

		timeout = MIN_TIMEOUT;



		tty_flip_buffer_push(tty);

	}



	return poll_mask;

}
@@ -688,8 +703,12 @@ int khvcd(void *unused) 
		if (!hvc_kicked) {

			if (poll_mask == 0)

				schedule();

			else

				msleep_interruptible(TIMEOUT);

			else {

				if (timeout < MAX_TIMEOUT)

					timeout += (timeout >> 6) + 1;



				msleep_interruptible(timeout);

			}

		}

		__set_current_state(TASK_RUNNING);

	} while (!kthread_should_stop());