Message-ID: <3A818BC4.7020007@magenta-netlogic.com>
Date: Wed, 07 Feb 2001 17:54:12 +0000
From: Tony Hoyle <tmh@magenta-netlogic.com>
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To: linux-kernel@vger.kernel.org
Subject: ACPI slowdown... 
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I've been trying to track down what makes ACPI kill the system in 2.4.1.

In the acpi_idle function (drivers/acpi/cpu.c), it seems to spend most 
of its time with interrupts disabled, only enabling them to check 
need_resched occasionally.

In the 'sleep1' state the following code is executed:

         for (;;) {
                 unsigned long time;
                 unsigned long diff;

                 __cli();
                 if (current->need_resched)
                         goto out;
                 time = acpi_read_pm_timer();
                 safe_halt();
                 diff = acpi_compare_pm_timers(time, acpi_read_pm_timer());
                 if (diff > acpi_c2_enter_latency
                     && acpi_max_c_state >= 2)
                         goto sleep2;
         }

This looks wrong to me.  It's basically looping with interrupts 
disabled.  I can't see how current->need_resched could be updated at 
all, so the loop will only terminate when the PM timer tells it to.

Isn't disabling interrupts a bad thing anyway?  Wouldn't it be better to 
leave them enabled (this is uniprocessor only so there shouldn't be 
concurrency issues).

Tony

-- 

The only secure computer is one that's unplugged, locked in a safe,
and buried 20 feet under the ground in a secret location... and i'm
not even too sure about that one"--Dennis Huges, FBI.

tmh@magenta-netlogic.com

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