linux-kernel - Re: [PATCH] Re: x86_32 tsc/pit and hrtimers

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Date:	Wed, 08 Oct 2008 17:47:53 -0400
From:	Chris Snook <csnook@...hat.com>
To:	Jeff Hansen <x@...fhansen.com>
CC:	torvalds@...ux-foundation.org, linux-kernel@...r.kernel.org,
	mingo@...e.hu
Subject: Re: [PATCH] Re: x86_32 tsc/pit and hrtimers

Jeff Hansen wrote:
> [HRTIMER]: Add highres=noverify option to bypass clocksource verification
> 
> This disregards the CLOCK_SOURCE_MUST_VERIFY flag on all clocksources.
> This is particularly useful on legacy x86_32 systems that have no ACPI,
> LAPIC, or HPET timers, where only TSC and PIT are available.
> 
> Thanks to Chris Snook for suggesting this.
> ---
>  include/linux/clocksource.h |    2 ++
>  kernel/hrtimer.c            |    2 ++
>  kernel/time/clocksource.c   |    3 ++-
>  3 files changed, 6 insertions(+), 1 deletions(-)

Please also update Documentation/kernel-parameters.txt, and resubmit with your 
Signed-off-by tag.

-- Chris

> diff --git a/include/linux/clocksource.h b/include/linux/clocksource.h
> index 55e434f..90ae835 100644
> --- a/include/linux/clocksource.h
> +++ b/include/linux/clocksource.h
> @@ -104,6 +104,8 @@ extern struct clocksource *clock;    /* current 
> clocksource */
>  #define CLOCK_SOURCE_WATCHDOG            0x10
>  #define CLOCK_SOURCE_VALID_FOR_HRES        0x20
> 
> +extern int clocksource_noverify;
> +
>  /* simplify initialization of mask field */
>  #define CLOCKSOURCE_MASK(bits) (cycle_t)((bits) < 64 ? 
> ((1ULL<<(bits))-1) : -1)
> 
> diff --git a/kernel/hrtimer.c b/kernel/hrtimer.c
> index ab80515..2fdf59f 100644
> --- a/kernel/hrtimer.c
> +++ b/kernel/hrtimer.c
> @@ -476,6 +476,8 @@ static int __init setup_hrtimer_hres(char *str)
>          hrtimer_hres_enabled = 0;
>      else if (!strcmp(str, "on"))
>          hrtimer_hres_enabled = 1;
> +    else if (!strcmp(str, "noverify"))
> +        clocksource_noverify = 1;
>      else
>          return 0;
>      return 1;
> diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c
> index dadde53..d3c14c1 100644
> --- a/kernel/time/clocksource.c
> +++ b/kernel/time/clocksource.c
> @@ -54,6 +54,7 @@ static LIST_HEAD(clocksource_list);
>  static DEFINE_SPINLOCK(clocksource_lock);
>  static char override_name[32];
>  static int finished_booting;
> +int clocksource_noverify;
> 
>  /* clocksource_done_booting - Called near the end of core bootup
>   *
> @@ -165,7 +166,7 @@ static void clocksource_check_watchdog(struct 
> clocksource *cs)
>      unsigned long flags;
> 
>      spin_lock_irqsave(&watchdog_lock, flags);
> -    if (cs->flags & CLOCK_SOURCE_MUST_VERIFY) {
> +    if (!clocksource_noverify && cs->flags & CLOCK_SOURCE_MUST_VERIFY) {
>          int started = !list_empty(&watchdog_list);
> 
>          list_add(&cs->wd_list, &watchdog_list);

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