Re: acpi_idle: Very idle Core i7 machine never enters C3

[Philip Langdale <philipl@overt.org>]

On Fri, 05 Feb 2010 12:45:21 -0500 (EST)
Len Brown <lenb@kernel.org> wrote:

> Jeff,
> What do you see if you apply just the patch below?
> 
> Also, in addition to "powertop -d" to show what the kernel requests,
> please run turbostat to show what the hardware actually did:
> 
> http://userweb.kernel.org/~lenb/acpi/utils/pmtools-latest/turbostat/turbostat.c
> 
> eg.
> # turbostat -d -v sleep 5
> 
> thanks,
> -Len Brown, Intel Open Source Technology Center
> ---

To resurrect this thread...

I have a giga-byte GA-P55M-UD4 motherboard and I have this same problem
as well. Len's patch "works" in that I see C6 being used, but it also
cripples the system - if I do a make -j16 kernel build, I see most jobs
serialized onto one or two cores. Without the patch, I see the
full utilization of all 8 hyper-threads as expected.

Now, gigabyte have already b0rked these boards up by using the UHCI
controllers on the PCH instead of the rate matching hubs. Maybe that's
directly the cause of BM activity - maybe they screwed something else
up - is it possible for BIOS/ACPI mistakes to lead to this behaviour?

Jeff - is your board gigabyte too?

--phil

> diff --git a/drivers/acpi/processor_idle.c
> b/drivers/acpi/processor_idle.c index 7c0441f..f528625 100644
> --- a/drivers/acpi/processor_idle.c
> +++ b/drivers/acpi/processor_idle.c
> @@ -763,7 +763,7 @@ static const struct file_operations
> acpi_processor_power_fops = { static int acpi_idle_bm_check(void)
>  {
>  	u32 bm_status = 0;
> -
> +return bm_status;
>  	acpi_read_bit_register(ACPI_BITREG_BUS_MASTER_STATUS,
> &bm_status); if (bm_status)
>  		acpi_write_bit_register(ACPI_BITREG_BUS_MASTER_STATUS,
> 1);
> 
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> 




--phil