linux-kernel - Re: [PATCH] x86: Export tsc related information in sysfs

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Date:	Sat, 15 May 2010 18:05:16 +0530
From:	Jaswinder Singh Rajput <jaswinderlinux@...il.com>
To:	Venkatesh Pallipadi <venki@...gle.com>
Cc:	Ingo Molnar <mingo@...e.hu>, Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Chris Mason <chris.mason@...cle.com>,
	linux-kernel@...r.kernel.org,
	Dan Magenheimer <dan.magenheimer@...cle.com>
Subject: Re: [PATCH] x86: Export tsc related information in sysfs

Hello,

On Sat, May 15, 2010 at 7:10 AM, Venkatesh Pallipadi <venki@...gle.com> wrote:
> From: Dan Magenheimer <dan.magenheimer@...cle.com>
>
> Kernel information about calibrated value of tsc_khz and
> tsc_stability (result of tsc warp test) are useful bits of information
> for any app that wants to use TSC directly. Export this read_only
> information in sysfs.
>
> Signed-off-by: Venkatesh Pallipadi <venki@...gle.com>
> Signed-off-by: Dan Magenheimer <dan.magenheimer@...cle.com>
> ---
>  arch/x86/kernel/tsc.c |   76 +++++++++++++++++++++++++++++++++++++++++++++++++
>  1 files changed, 76 insertions(+), 0 deletions(-)
>
> diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
> index 9faf91a..24dd484 100644
> --- a/arch/x86/kernel/tsc.c
> +++ b/arch/x86/kernel/tsc.c
> @@ -10,6 +10,7 @@
>  #include <linux/clocksource.h>
>  #include <linux/percpu.h>
>  #include <linux/timex.h>
> +#include <linux/sysdev.h>
>
>  #include <asm/hpet.h>
>  #include <asm/timer.h>
> @@ -857,6 +858,81 @@ static void __init init_tsc_clocksource(void)
>        clocksource_register(&clocksource_tsc);
>  }
>
> +#ifdef CONFIG_SYSFS
> +/*
> + * Export TSC related info to user land. This reflects kernel usage of TSC
> + * as hints to userspace users of TSC. The read_only info provided here:
> + * - tsc_stable: 1 implies system has TSC that always counts at a constant
> + *   rate, sync across CPUs and has passed the kernel warp test.
> + * - tsc_khz: TSC frequency in khz.
> + * - tsc_mult and tsc_shift: multiplier and shift to optimally convert
> + *   TSC delta to ns; ns = ((u64) delta * mult) >> shift
> + */
> +
> +#define define_show_var_function(_name, _var) \
> +static ssize_t show_##_name( \
> +       struct sys_device *dev, struct sysdev_attribute *attr, char *buf) \
> +{ \
> +       return sprintf(buf, "%u\n", (unsigned int) _var);\
> +}
> +
> +define_show_var_function(tsc_stable, !tsc_unstable);
> +define_show_var_function(tsc_khz, tsc_khz);
> +define_show_var_function(tsc_mult, clocksource_tsc.mult);
> +define_show_var_function(tsc_shift, clocksource_tsc.shift);
> +
> +static SYSDEV_ATTR(tsc_stable, 0444, show_tsc_stable, NULL);
> +static SYSDEV_ATTR(tsc_khz, 0444, show_tsc_khz, NULL);
> +static SYSDEV_ATTR(tsc_mult, 0444, show_tsc_mult, NULL);
> +static SYSDEV_ATTR(tsc_shift, 0444, show_tsc_shift, NULL);
> +
> +static struct sysdev_attribute *tsc_attrs[] = {
> +       &attr_tsc_stable,
> +       &attr_tsc_khz,
> +       &attr_tsc_mult,
> +       &attr_tsc_shift,
> +};
> +
> +static struct sysdev_class tsc_sysclass = {
> +       .name = "tsc",
> +};
> +
> +static struct sys_device device_tsc = {
> +       .id = 0,
> +       .cls = &tsc_sysclass,
> +};
> +
> +static int __init init_tsc_sysfs(void)
> +{
> +       int err, i = 0;
> +
> +       err = sysdev_class_register(&tsc_sysclass);
> +       if (err)
> +               return err;
> +
> +       err = sysdev_register(&device_tsc);
> +       if (err)
> +               goto fail;

fail will call sysdev_unregister(&device_tsc) which is not
appropriate, please fix this goto.

Thanks,
--
Jaswinder Singh.

> +
> +       for (i = 0; i < ARRAY_SIZE(tsc_attrs); i++) {
> +               err = sysdev_create_file(&device_tsc, tsc_attrs[i]);
> +               if (err)
> +                       goto fail;
> +       }
> +
> +       return 0;
> +
> +fail:
> +       while (--i >= 0)
> +               sysdev_remove_file(&device_tsc, tsc_attrs[i]);
> +
> +       sysdev_unregister(&device_tsc);
> +       sysdev_class_unregister(&tsc_sysclass);
> +       return err;
> +}
> +device_initcall(init_tsc_sysfs);
> +#endif
> +
>  #ifdef CONFIG_X86_64
>  /*
>  * calibrate_cpu is used on systems with fixed rate TSCs to determine
> --
> 1.7.0.1
>
> --
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