Prev: Per-superblock shrinkers
Next: NOTIFICATION!
From: Venkatesh Pallipadi on 14 May 2010 21:50
From: Dan Magenheimer <dan.magenheimer(a)oracle.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(a)google.com>
Signed-off-by: Dan Magenheimer <dan.magenheimer(a)oracle.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;
+
+ 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

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo(a)vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
 | 
Pages: 1
Prev: Per-superblock shrinkers
Next: NOTIFICATION!