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[POWERPC] hvc_console: Polling mode timer backoff

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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: Will Schmidt <will_schmidt@vnet.ibm.com>
Signed-off-by: Michael Ellerman <michael@ellerman.id.au>
Acked-by: Linas Vepstas <linas@austin.ibm.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>
This commit is contained in:
Will Schmidt 2007-04-18 00:44:46 +10:00 committed by Paul Mackerras
parent b3a6d2a54b
commit b791072ba3
1 changed files with 25 additions and 6 deletions
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31
drivers/char/hvc_console.c
View file

@ -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
@ -642,9 +652,14 @@ 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());