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Date: Sun, 11 Feb 2001 23:04:48 +0100
From: Pavel Machek <pavel@suse.cz>
To: Tony Hoyle <tmh@magenta-netlogic.com>
Cc: linux-kernel@vger.kernel.org
Subject: Re: ACPI slowdown...
In-Reply-To: <3A818BC4.7020007@magenta-netlogic.com> <3A81920A.90601@magenta-netlogic.com>
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In-Reply-To: <3A81920A.90601@magenta-netlogic.com>; from Tony Hoyle on Wed, Feb 07, 2001 at 06:20:58PM +0000
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Hi!

> Tony Hoyle wrote:
> 
> I'm talking to myself :-)
> 
> OK I see that safe_halt() will re-enable interrupts.  However this is only
> called in S1.  If your machine gets as far as S3 you have...
> 
>          for (;;) {
>                  unsigned long time;
>                  unsigned long diff;
> 
>                  __cli();
>                  if (current->need_resched)
>                          goto out;
>                  if (acpi_bm_activity())
>                          goto sleep2;
> 
>                  time = acpi_read_pm_timer();
>                  inb(acpi_pblk + ACPI_P_LVL3);
>                  /* Dummy read, force synchronization with the PMU */
>                  acpi_read_pm_timer();
>                  diff = acpi_compare_pm_timers(time, acpi_read_pm_timer());
> 
>                  __sti();
>                  if (diff < acpi_c3_exit_latency)
>                          goto sleep2;
>          }
> 
> There is no halt here... the interrupts are enabled for only a couple of 
> instructions (one comparison and a jump) before being disabled again. 
> It seems to me if the computer gets into S3 it'll effectively die until 
> some kind of busmaster device wakes it up (DMA?).

No.

If interrupts come in cli-ed section, it will be postponed until
sti. It then comes, and sets need_resched and recovers.

								Pavel
-- 
I'm pavel@ucw.cz. "In my country we have almost anarchy and I don't care."
Panos Katsaloulis describing me w.r.t. patents at discuss@linmodems.org
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