linux-kernel - Re: tsc breaks atkbd suspend

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Date:	Mon, 18 Feb 2008 15:26:10 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Pavel Machek <pavel@....cz>
cc:	kernel list <linux-kernel@...r.kernel.org>, jikos@...e.cz,
	Ingo Molnar <mingo@...e.hu>, "Rafael J. Wysocki" <rjw@...k.pl>,
	Andrew Morton <akpm@...l.org>
Subject: Re: tsc breaks atkbd suspend

On Mon, 18 Feb 2008, Pavel Machek wrote:
> Hi!
> 
> I'm trying to use the "sleepy test" here, unfortunately it locks for
> 10-or-so seconds.
> 
> Problem is in wait_event_timeout: timeouts take about 100x as long as
> they should. Code in drivers/input/serio/libps2.c:
> 
> +       printk("ps2_command waiting event: %d\n", timeout);
>         timeout = wait_event_timeout(ps2dev->wait,
>                                      !(ps2dev->flags & PS2_FLAG_CMD1),timeout);
> 
>         if (ps2dev->cmdcnt && timeout > 0) {
> +               printk("wait_event returned: %d\n", timeout);
> 
>                 timeout = ps2_adjust_timeout(ps2dev, command, timeout);
> +
> +               printk("ps2_command adjust timeout: %d\n", timeout);
>                 wait_event_timeout(ps2dev->wait,
>                                    !(ps2dev->flags & PS2_FLAG_CMD), timeout);
>         }
> 
> +       printk("ps2_command receiving\n");
> 
> 
> ...and I get hang after "ps2_command adjust timeout" for 10 seconds,
> while it should  wait 10msec or so.

When is this code called ?
 
> I even tried adding:
> 
> +       printk("ps2: testing timeouts\n");
> +       timeout = wait_event_timeout(ps2dev->wait, 0, 10);
> +       printk("ps2: testing timeouts\n");
> +       timeout = wait_event_timeout(ps2dev->wait, 0, 10);
> +       printk("ps2: testing timeouts\n");
> +       timeout = wait_event_timeout(ps2dev->wait, 0, 10);
> +       printk("ps2: testing timeouts\n");
> +       timeout = wait_event_timeout(ps2dev->wait, 0, 10);
> +       printk("ps2: testing timeouts\n");
> +       timeout = wait_event_timeout(ps2dev->wait, 0, 10);
> +       printk("ps2: timeouts ok?\n");
> 
> before that, and yes, those wait too long, too... (but only during
> suspend, they work ok during boot).

Again, at which point during suspend is this ?
 
> nohz=off fixes that.
> 
> notsc fixes that, too... On my system (thinkpad x60 in UP mode) tsc is
> normally marked unstable very shortly after boot, so only sleepy test
> can trigger this.

I do not understand, what you mean. When exactly is "sleeppy test"
running ?

Also the TSC unstable detection is in a 500ms timeframe, so you should
never get a 10s delay.

> I believe it is very bad idea to use tsc, it does not work on 90%+ of
> machines. Yes, we do detect it is broken during runtime, but that's
> too late.

Why is it too late ? Can you please describe in detail ?

> I believe fix is very simple:

NAK. 

This kills TSC on machines which have a working TSC and never go into
suspend.

	tglx
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