[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: 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>
diff --git a/drivers/char/hvc_console.c b/drivers/char/hvc_console.c
index a0a88aa2..fc9bc77 100644
--- a/drivers/char/hvc_console.c
+++ b/drivers/char/hvc_console.c
@@ -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 @@
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 @@
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 @@
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());