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x86, tsc, sched: Recompute cyc2ns_offset's during resume from sleep states 

TSC's get reset after suspend/resume (even on cpu's with invariant TSC
which runs at a constant rate across ACPI P-, C- and T-states). And in
some systems BIOS seem to reinit TSC to arbitrary large value (still
sync'd across cpu's) during resume.

This leads to a scenario of scheduler rq->clock (sched_clock_cpu()) less
than rq->age_stamp (introduced in 2.6.32). This leads to a big value
returned by scale_rt_power() and the resulting big group power set by the
update_group_power() is causing improper load balancing between busy and
idle cpu's after suspend/resume.

This resulted in multi-threaded workloads (like kernel-compilation) go
slower after suspend/resume cycle on core i5 laptops.

Fix this by recomputing cyc2ns_offset's during resume, so that
sched_clock() continues from the point where it was left off during
suspend.

Reported-by: Florian Pritz <flo@xssn.at>
Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
Cc: <stable@kernel.org> # [v2.6.32+]
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <1282262618.2675.24.camel@sbsiddha-MOBL3.sc.intel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Suresh Siddha 2010-08-19 17:03:38 -07:00 committed by Ingo Molnar
parent 861d034ee8
commit cd7240c0b9
3 changed files with 42 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
arch/x86/include/asm/tsc.h
View File

@ -59,5 +59,7 @@ extern void check_tsc_sync_source(int cpu);
extern void check_tsc_sync_target(void);
extern int notsc_setup(char *);
extern void save_sched_clock_state(void);
extern void restore_sched_clock_state(void);
#endif /* _ASM_X86_TSC_H */

38
arch/x86/kernel/tsc.c
View File

@ -626,6 +626,44 @@ static void set_cyc2ns_scale(unsigned long cpu_khz, int cpu)
local_irq_restore(flags);
}
static unsigned long long cyc2ns_suspend;
void save_sched_clock_state(void)
{
if (!sched_clock_stable)
return;
cyc2ns_suspend = sched_clock();
}
/*
* Even on processors with invariant TSC, TSC gets reset in some the
* ACPI system sleep states. And in some systems BIOS seem to reinit TSC to
* arbitrary value (still sync'd across cpu's) during resume from such sleep
* states. To cope up with this, recompute the cyc2ns_offset for each cpu so
* that sched_clock() continues from the point where it was left off during
* suspend.
*/
void restore_sched_clock_state(void)
{
unsigned long long offset;
unsigned long flags;
int cpu;
if (!sched_clock_stable)
return;
local_irq_save(flags);
get_cpu_var(cyc2ns_offset) = 0;
offset = cyc2ns_suspend - sched_clock();
for_each_possible_cpu(cpu)
per_cpu(cyc2ns_offset, cpu) = offset;
local_irq_restore(flags);
}
#ifdef CONFIG_CPU_FREQ
/* Frequency scaling support. Adjust the TSC based timer when the cpu frequency

2
arch/x86/power/cpu.c
View File

@ -113,6 +113,7 @@ static void __save_processor_state(struct saved_context *ctxt)
void save_processor_state(void)
{
__save_processor_state(&saved_context);
save_sched_clock_state();
}
#ifdef CONFIG_X86_32
EXPORT_SYMBOL(save_processor_state);
@ -229,6 +230,7 @@ static void __restore_processor_state(struct saved_context *ctxt)
void restore_processor_state(void)
{
__restore_processor_state(&saved_context);
restore_sched_clock_state();
}
#ifdef CONFIG_X86_32
EXPORT_SYMBOL(restore_processor_state);