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SubjectRe: [PATCH] Re: x86_32 tsc/pit and hrtimers
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On Thu, 2008-10-09 at 14:18 -0700, Jeff Hansen wrote:
> [X86] Add tsc=stable option for marking TSC as stable
>
> This enables legacy hardware or VMs without HPET, LAPIC, or ACPI
> timers to enter high-resolution timer mode.
>
> Signed-off-by: Jeff Hansen <jhansen@cardaccess-inc.com>
> ---
> Documentation/kernel-parameters.txt | 4 ++++
> arch/x86/kernel/tsc_32.c | 12 +++++++++++-
> arch/x86/kernel/tsc_64.c | 9 +++++++++
> 3 files changed, 24 insertions(+), 1 deletions(-)

Hi Jeff,

I see that these changes are not for the mainline tree. Do you plan to
do something of this sought for mainline (.28/tip) ?

My comments below are mainly for generalizing this stuff, don't know how
useful these (my comments) will be for 26.5


> diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
> index 9611505..8488074 100644
> --- a/Documentation/kernel-parameters.txt
> +++ b/Documentation/kernel-parameters.txt
> @@ -2084,6 +2084,10 @@ and is between 256 and 4096 characters. It is defined in the file
> Format:
> <io>,<irq>,<dma>,<dma2>,<sb_io>,<sb_irq>,<sb_dma>,<mpu_io>,<mpu_irq>
>
> + tsc= [X86-32,X86-64]
> + tsc=stable: Mark TSC clocksource as stable, enabling
> + high-resolution timer mode on older hardware.
> +
> turbografx.map[2|3]= [HW,JOY]
> TurboGraFX parallel port interface
> Format:
> diff --git a/arch/x86/kernel/tsc_32.c b/arch/x86/kernel/tsc_32.c
> index 65b7063..f6e8f71 100644
> --- a/arch/x86/kernel/tsc_32.c
> +++ b/arch/x86/kernel/tsc_32.c
> @@ -49,6 +49,17 @@ static int __init tsc_setup(char *str)
>
> __setup("notsc", tsc_setup);
>
> +static struct clocksource clocksource_tsc;
> +
> +static int __init tscx_setup(char *str)
> +{
> + if (!strcmp(str, "stable"))
> + clocksource_tsc.flags &= ~CLOCK_SOURCE_MUST_VERIFY;

Should we add a flag here instead, say tsc_reliable ? or whatever else
you want to call that.

Also, there is code in check_geode_tsc_reliable which too sets this flag
for the TSC clocksource.
Maybe you can just set the tsc_reliable flag from tscx_setup and
check_geode_tsc_reliable, and then check "tsc_reliable" value and set
the verify flag in init_tsc_clocksource.

Thanks,
Alok





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