[PATCH 28/28] Add a sched_clock paravirt_op

Jeremy Fitzhardinge
2007-04-14T21:21:43Z

[-- Attachment #1: paravirt-sched-clock-ff.patch --]
[-- Type: text/plain, Size: 8105 bytes --]

The tsc-based get_scheduled_cycles interface is not a good match for
Xen's runstate accounting, which reports everything in nanoseconds.

This patch replaces this interface with a sched_clock interface, which
matches both Xen and VMI's requirements.

In order to do this, we:
1. replace get_scheduled_cycles with sched_clock
2. hoist cycles_2_ns into a common header
3. update vmi accordingly

One thing to note: because sched_clock is implemented as a weak
function in kernel/sched.c, we must define a real function in order to
override this weak binding. This means the usual paravirt_ops
technique of using an inline function won't work in this case.

Signed-off-by: Jeremy Fitzhardinge <jeremy@xensource.com>
Cc: Zachary Amsden <zach@vmware.com>
Cc: Dan Hecht <dhecht@vmware.com>
Cc: john stultz <johnstul@us.ibm.com>

---
arch/i386/kernel/paravirt.c | 2 -
arch/i386/kernel/sched-clock.c | 43 ++++++++++++++-----------------------
arch/i386/kernel/vmi.c | 2 -
arch/i386/kernel/vmiclock.c | 6 ++---
include/asm-i386/paravirt.h | 7 ++++--
include/asm-i386/timer.h | 46 +++++++++++++++++++++++++++++++++++++++-
include/asm-i386/vmi_time.h | 2 -
7 files changed, 73 insertions(+), 35 deletions(-)

===================================================================
--- a/arch/i386/kernel/paravirt.c
+++ b/arch/i386/kernel/paravirt.c
@@ -268,7 +268,7 @@ struct paravirt_ops paravirt_ops = {
.write_msr = native_write_msr_safe,
.read_tsc = native_read_tsc,
.read_pmc = native_read_pmc,
- .get_scheduled_cycles = native_read_tsc,
+ .sched_clock = native_sched_clock,
.get_cpu_khz = native_calculate_cpu_khz,
.load_tr_desc = native_load_tr_desc,
.set_ldt = native_set_ldt,
===================================================================
--- a/arch/i386/kernel/sched-clock.c
+++ b/arch/i386/kernel/sched-clock.c
@@ -35,28 +35,7 @@
* -johnstul@us.ibm.com "math is hard, lets go shopping!"
*/

-#define CYC2NS_SCALE_FACTOR 10 /* 2^10, carefully chosen */
-
-struct sc_data {
- unsigned int cyc2ns_scale;
- unsigned long long sync_tsc;
- unsigned long long ns_base;
- unsigned long long last_val;
- unsigned long long sync_jiffies;
-};
-
-static DEFINE_PER_CPU(struct sc_data, sc_data);
-
-static inline unsigned long long cycles_2_ns(struct sc_data *sc, unsigned long long cyc)
-{
- unsigned long long ns;
-
- cyc -= sc->sync_tsc;
- ns = (cyc * sc->cyc2ns_scale) >> CYC2NS_SCALE_FACTOR;
- ns += sc->ns_base;
-
- return ns;
-}
+DEFINE_PER_CPU(struct sc_data, sc_data);

/*
* Scheduler clock - returns current time in nanosec units.
@@ -66,7 +45,7 @@ static inline unsigned long long cycles_
* [1] no attempt to stop CPU instruction reordering, which can hit
* in a 100 instruction window or so.
*/
-unsigned long long sched_clock(void)
+unsigned long long native_sched_clock(void)
{
unsigned long long r;
struct sc_data *sc = &get_cpu_var(sc_data);
@@ -81,8 +60,8 @@ unsigned long long sched_clock(void)
sc->last_val = r;
local_irq_restore(flags);
} else {
- get_scheduled_cycles(r);
- r = cycles_2_ns(sc, r);
+ rdtscll(r);
+ r = cycles_2_ns(r);
sc->last_val = r;
}

@@ -90,6 +69,18 @@ unsigned long long sched_clock(void)

return r;
}
+
+/* We need to define a real function for sched_clock, to override the
+ weak default version */
+#ifdef CONFIG_PARAVIRT
+unsigned long long sched_clock(void)
+{
+ return paravirt_sched_clock();
+}
+#else
+unsigned long long sched_clock(void)
+ __attribute__((alias("native_sched_clock")));
+#endif

/* Resync with new CPU frequency */
static void resync_sc_freq(struct sc_data *sc, unsigned int newfreq)
@@ -103,7 +94,7 @@ static void resync_sc_freq(struct sc_dat
because sched_clock callers should be able to tolerate small
errors. */
sc->ns_base = ktime_to_ns(ktime_get());
- get_scheduled_cycles(sc->sync_tsc);
+ rdtscll(sc->sync_tsc);
sc->cyc2ns_scale = (1000000 << CYC2NS_SCALE_FACTOR) / newfreq;
}

===================================================================
--- a/arch/i386/kernel/vmi.c
+++ b/arch/i386/kernel/vmi.c
@@ -887,7 +887,7 @@ static inline int __init activate_vmi(vo
paravirt_ops.setup_boot_clock = vmi_time_bsp_init;
paravirt_ops.setup_secondary_clock = vmi_time_ap_init;
#endif
- paravirt_ops.get_scheduled_cycles = vmi_get_sched_cycles;
+ paravirt_ops.sched_clock = vmi_sched_clock;
paravirt_ops.get_cpu_khz = vmi_cpu_khz;

/* We have true wallclock functions; disable CMOS clock sync */
===================================================================
--- a/arch/i386/kernel/vmiclock.c
+++ b/arch/i386/kernel/vmiclock.c
@@ -65,9 +65,9 @@ int vmi_set_wallclock(unsigned long now)
}

/* paravirt_ops.get_scheduled_cycles = vmi_get_sched_cycles */
-unsigned long long vmi_get_sched_cycles(void)
-{
- return vmi_timer_ops.get_cycle_counter(VMI_CYCLES_AVAILABLE);
+unsigned long long vmi_sched_clock(void)
+{
+ return cycles_2_ns(vmi_timer_ops.get_cycle_counter(VMI_CYCLES_AVAILABLE));
}

/* paravirt_ops.get_cpu_khz = vmi_cpu_khz */
===================================================================
--- a/include/asm-i386/paravirt.h
+++ b/include/asm-i386/paravirt.h
@@ -116,7 +116,7 @@ struct paravirt_ops

u64 (*read_tsc)(void);
u64 (*read_pmc)(void);
- u64 (*get_scheduled_cycles)(void);
+ unsigned long long (*sched_clock)(void);
unsigned long (*get_cpu_khz)(void);

/* Segment descriptor handling */
@@ -573,7 +573,10 @@ static inline u64 paravirt_read_tsc(void

#define rdtscll(val) (val = paravirt_read_tsc())

-#define get_scheduled_cycles(val) (val = paravirt_ops.get_scheduled_cycles())
+static inline unsigned long long paravirt_sched_clock(void)
+{
+ return PVOP_CALL0(unsigned long long, sched_clock);
+}
#define calculate_cpu_khz() (paravirt_ops.get_cpu_khz())

#define write_tsc(val1,val2) wrmsr(0x10, val1, val2)
===================================================================
--- a/include/asm-i386/timer.h
+++ b/include/asm-i386/timer.h
@@ -15,8 +15,52 @@ extern int recalibrate_cpu_khz(void);
extern int recalibrate_cpu_khz(void);

#ifndef CONFIG_PARAVIRT
-#define get_scheduled_cycles(val) rdtscll(val)
#define calculate_cpu_khz() native_calculate_cpu_khz()
#endif

+/* Accellerators for sched_clock()
+ * convert from cycles(64bits) => nanoseconds (64bits)
+ * basic equation:
+ * ns = cycles / (freq / ns_per_sec)
+ * ns = cycles * (ns_per_sec / freq)
+ * ns = cycles * (10^9 / (cpu_khz * 10^3))
+ * ns = cycles * (10^6 / cpu_khz)
+ *
+ * Then we use scaling math (suggested by george@mvista.com) to get:
+ * ns = cycles * (10^6 * SC / cpu_khz) / SC
+ * ns = cycles * cyc2ns_scale / SC
+ *
+ * And since SC is a constant power of two, we can convert the div
+ * into a shift.
+ *
+ * We can use khz divisor instead of mhz to keep a better percision, since
+ * cyc2ns_scale is limited to 10^6 * 2^10, which fits in 32 bits.
+ * (mathieu.desnoyers@polymtl.ca)
+ *
+ * -johnstul@us.ibm.com "math is hard, lets go shopping!"
+ */
+struct sc_data {
+ unsigned int cyc2ns_scale;
+ unsigned long long sync_tsc;
+ unsigned long long ns_base;
+ unsigned long long last_val;
+ unsigned long long sync_jiffies;
+};
+
+DECLARE_PER_CPU(struct sc_data, sc_data);
+
+#define CYC2NS_SCALE_FACTOR 10 /* 2^10, carefully chosen */
+
+static inline unsigned long long cycles_2_ns(unsigned long long cyc)
+{
+ const struct sc_data *sc = &__get_cpu_var(sc_data);
+ unsigned long long ns;
+
+ cyc -= sc->sync_tsc;
+ ns = (cyc * sc->cyc2ns_scale) >> CYC2NS_SCALE_FACTOR;
+ ns += sc->ns_base;
+
+ return ns;
+}
+
#endif
===================================================================
--- a/include/asm-i386/vmi_time.h
+++ b/include/asm-i386/vmi_time.h
@@ -49,7 +49,7 @@ extern void __init vmi_time_init(void);
extern void __init vmi_time_init(void);
extern unsigned long vmi_get_wallclock(void);
extern int vmi_set_wallclock(unsigned long now);
-extern unsigned long long vmi_get_sched_cycles(void);
+extern unsigned long long vmi_sched_clock(void);
extern unsigned long vmi_cpu_khz(void);

#ifdef CONFIG_X86_LOCAL_APIC

--