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For freqency dependent TSCs we only scale the cycles, we do not account
for the discrepancy in absolute value.
Our current formula is: time = cycles * mult
(where mult is a function of the cpu-speed on variable tsc machines)
Suppose our current cycle count is 10, and we have a multiplier of 5,
then our time value would end up being 50.
Now cpufreq comes along and changes the multiplier to say 3 or 7,
which would result in our time being resp. 30 or 70.
That means that we can observe random jumps in the time value due to
frequency changes in both fwd and bwd direction.
So what this patch does is change the formula to:
time = cycles * frequency + offset
And we calculate offset so that time_before == time_after, thereby
ridding us of these jumps in time.
[ Impact: fix/reduce sched_clock() jumps across frequency changing events ]
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Chucked-on-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
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Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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Impact: cleanup
Make x86_quirks support more transparent. The highlevel
methods are now named:
extern void x86_quirk_pre_intr_init(void);
extern void x86_quirk_intr_init(void);
extern void x86_quirk_trap_init(void);
extern void x86_quirk_pre_time_init(void);
extern void x86_quirk_time_init(void);
This makes it clear that if some platform extension has to
do something here that it is considered ... weird, and is
discouraged.
Also remove arch_hooks.h and move it into setup.h (and other
header files where appropriate).
Signed-off-by: Ingo Molnar <mingo@elte.hu>
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Change header guards named "ASM_X86__*" to "_ASM_X86_*" since:
a. the double underscore is ugly and pointless.
b. no leading underscore violates namespace constraints.
Signed-off-by: H. Peter Anvin <hpa@zytor.com>
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Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>
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