Hi,

I noticed on one of my systems that powertop was showing events/0 waking
at a high rate (~2000 times/sec, HZ=1000).  After a lot of tracing I
found it was due to writes pending to ptys which hadn't been read.

Specifically, in flush_to_ldisc(), these lines seem to be causing the
repeated wakeups:

			if (!tty->receive_room) {
				schedule_delayed_work(&tty->buf.work, 1);
				break;
			}

After reading the pending writes the system settles down and wakeups
drops to a normal low level.

The program provoking this was Xen's xenconsoled, which manages running
domains' consoles; the unread output was various domains console
output.  This doesn't seem to be related to Xen at all: Ian Jackson put
together a small standalone program (attached) which reproduces the
problem; he reports that this wakeup behaviour is a regression compared
to a 2.6.16 Debian kernel.

Compile ptypolling with: gcc -o ptypolling ptypolling.c -g -lutil

After running ptypolling, powertop shows events/0 waking at a high
rate.  ptypolling itself is blocked in a select() and is idle.

Thanks,
    J