[v4,2/4] Always running timer correlated clocksource

On modern Intel systems TSC is derived from the new Always Running Timer
(ART). In addition, ART can be captured simultaneous to the capture of
audio and network device clocks, allowing a correlation between timebases
to be constructed. Upon capture, the driver converts the captured ART
value to the appropriate system clock using the correlated clocksource
mechanism.

On systems that support ART a new CPUID leaf (0x15) returns parameters
“m” and “n” such that:

TSC_value = (ART_value * m) / n + k [n >= 2]

[k is an offset that can adjusted by a privileged agent. The
IA32_TSC_ADJUST MSR is an example of an interface to adjust k.
See 17.14.4 of the Intel SDM for more details]

Signed-off-by: Christopher S. Hall <christopher.s.hall@intel.com>
---
 arch/x86/include/asm/cpufeature.h |  2 +-
 arch/x86/include/asm/tsc.h        |  2 ++
 arch/x86/kernel/tsc.c             | 48 ++++++++++++++++++++++++++++++++++++++-
 3 files changed, 50 insertions(+), 2 deletions(-)

Hi Christopher,

[auto build test ERROR on net/master -- if it's inappropriate base, please suggest rules for selecting the more suitable base]

url:    https://github.com/0day-ci/linux/commits/Christopher-S-Hall/Patchset-enabling-hardware-based-cross-timestamps-for-next-gen-Intel-platforms/20151013-095135
config: x86_64-randconfig-x015-10130227 (attached as .config)
reproduce:
        # save the attached .config to linux build tree
        make ARCH=x86_64 

All errors (new ones prefixed by >>):

   arch/x86/kernel/tsc.c: In function 'convert_art_to_tsc':
>> arch/x86/kernel/tsc.c:1098:18: error: 'art_to_tsc_denominator' undeclared (first use in this function)
     res = (cycles / art_to_tsc_denominator) * art_to_tsc_numerator;
                     ^
   arch/x86/kernel/tsc.c:1098:18: note: each undeclared identifier is reported only once for each function it appears in
>> arch/x86/kernel/tsc.c:1098:44: error: 'art_to_tsc_numerator' undeclared (first use in this function)
     res = (cycles / art_to_tsc_denominator) * art_to_tsc_numerator;
                                               ^

vim +/art_to_tsc_denominator +1098 arch/x86/kernel/tsc.c

  1092	 * Convert ART to TSC given numerator/denominator found in detect_art()
  1093	 */
  1094	static u64 convert_art_to_tsc(struct correlated_cs *cs, u64 cycles)
  1095	{
  1096		u64 tmp, res;
  1097	
> 1098		res = (cycles / art_to_tsc_denominator) * art_to_tsc_numerator;
  1099		tmp = (cycles % art_to_tsc_denominator) * art_to_tsc_numerator;
  1100		res += tmp / art_to_tsc_denominator;
  1101	

---
0-DAY kernel test infrastructure                Open Source Technology Center
https://lists.01.org/pipermail/kbuild-all                   Intel Corporation

On Mon, 12 Oct 2015 11:45:20 -0700
"Hall, Christopher S" <christopher.s.hall@intel.com> wrote:
took a while to read the code, i have a few comments/questions
>
> diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
> index c3f7602..c3f098c 100644
> --- a/arch/x86/kernel/tsc.c
> +++ b/arch/x86/kernel/tsc.c
> @@ -820,7 +820,7 @@ int recalibrate_cpu_khz(void)
>  #ifndef CONFIG_SMP
This code is used by old p4/k7 clock modulation driver, why do we care?

>         unsigned long cpu_khz_old = cpu_khz;
> 
> -       if (cpu_has_tsc) {
> +       if (boot_cpu_has(X86_FEATURE_ART)) {
>                 tsc_khz = x86_platform.calibrate_tsc();
>                 cpu_khz = tsc_khz;
>                 cpu_data(0).loops_per_jiffy =


> 
> +/*
> + * Convert ART to TSC given numerator/denominator found in
> detect_art()
> + */
> +static u64 convert_art_to_tsc(struct correlated_cs *cs, u64 cycles)
> +{
> +       u64 tmp, res;
> +
> +       res = (cycles / art_to_tsc_denominator) *
> art_to_tsc_numerator;
> +       tmp = (cycles % art_to_tsc_denominator) *
> art_to_tsc_numerator;
> +       res += tmp / art_to_tsc_denominator;
> +
iirc there are some issues with 32bit, better use div64_u64()
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