> I tried extrapolating from t->stime_local_stamp, cpu_khz, and
> t->local_tsc_stamp before I got into the current solution. It would still
> bring accumulating skew, but in a slower increasing speed. I would like to
> try it again with t->tsc_scale instead of cpu_khz. If it is works, it would
> really be simpler. Allow me some time.
Below patch should be what you expected. It will still bring continuously
increasing tsc skew. If I pin all domains' vcpus on 1 pcpu, the skew is
increasing faster.
diff -r 1b173394f815 xen/arch/x86/acpi/cpu_idle.c
--- a/xen/arch/x86/acpi/cpu_idle.c Thu Dec 04 16:36:43 2008 +0000
+++ b/xen/arch/x86/acpi/cpu_idle.c Fri Dec 05 19:06:06 2008 +0800
@@ -317,8 +317,6 @@ static void acpi_processor_idle(void)
* stopped by H/W. Without carefully handling of TSC/APIC stop issues,
* deep C state can't work correctly.
*/
- /* preparing TSC stop */
- cstate_save_tsc();
/* preparing APIC stop */
lapic_timer_off();
diff -r 1b173394f815 xen/arch/x86/time.c
--- a/xen/arch/x86/time.c Thu Dec 04 16:36:43 2008 +0000
+++ b/xen/arch/x86/time.c Fri Dec 05 19:06:06 2008 +0800
@@ -48,11 +48,9 @@ struct time_scale {
struct cpu_time {
u64 local_tsc_stamp;
- u64 cstate_tsc_stamp;
s_time_t stime_local_stamp;
s_time_t stime_master_stamp;
struct time_scale tsc_scale;
- u64 cstate_plt_count_stamp;
};
struct platform_timesource {
@@ -149,6 +147,32 @@ static inline u64 scale_delta(u64 delta,
#endif
return product;
+}
+
+/*
+ * Scale a 32-bit time delta to delta by dividing a 32-bit fraction & scaling,
+ * yielding a 64-bit result.
+ */
+static inline u64 scale_time(u32 time_delta, struct time_scale *scale)
+{
+ u64 td64 = time_delta;
+ u64 quotient, remainder;
+
+ td64 <<= 32;
+
+ quotient = td64 / scale->mul_frac;
+ remainder = td64 % scale->mul_frac;
+
+ if ( scale->shift < 0 )
+ {
+ quotient <<= -scale->shift;
+ remainder <<= -scale->shift;
+ quotient += remainder / scale->mul_frac;
+ }
+ else
+ quotient >>= scale->shift;
+
+ return quotient;
}
/*
@@ -644,29 +668,19 @@ static void init_platform_timer(void)
freq_string(pts->frequency), pts->name);
}
-void cstate_save_tsc(void)
+void cstate_restore_tsc(void)
{
struct cpu_time *t = &this_cpu(cpu_time);
+ u64 tsc_delta;
+ s_time_t stime_delta;
if ( tsc_invariant )
return;
- t->cstate_plt_count_stamp = plt_src.read_counter();
- rdtscll(t->cstate_tsc_stamp);
-}
-
-void cstate_restore_tsc(void)
-{
- struct cpu_time *t = &this_cpu(cpu_time);
- u64 plt_count_delta, tsc_delta;
-
- if ( tsc_invariant )
- return;
-
- plt_count_delta = (plt_src.read_counter() -
- t->cstate_plt_count_stamp) & plt_mask;
- tsc_delta = scale_delta(plt_count_delta, &plt_scale) * cpu_khz/1000000UL;
- wrmsrl(MSR_IA32_TSC, t->cstate_tsc_stamp + tsc_delta);
+ stime_delta = read_platform_stime() - t->stime_local_stamp;
+ ASSERT(stime_delta < 0x100000000UL);
+ tsc_delta = scale_time((u32)stime_delta, &t->tsc_scale);
+ wrmsrl(MSR_IA32_TSC, t->local_tsc_stamp + tsc_delta);
}
/***************************************************************************
diff -r 1b173394f815 xen/include/xen/time.h
--- a/xen/include/xen/time.h Thu Dec 04 16:36:43 2008 +0000
+++ b/xen/include/xen/time.h Fri Dec 05 19:06:06 2008 +0800
@@ -13,7 +13,6 @@
#include <asm/time.h>
extern int init_xen_time(void);
-extern void cstate_save_tsc(void);
extern void cstate_restore_tsc(void);
extern unsigned long cpu_khz;
Jimmy
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