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arm64: Don't trace __switch_to if function graph tracer is enabled

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Function graph tracer shows negative time (wrap around) when tracing
__switch_to if the nosleep-time trace option is enabled.

Time compensation for nosleep-time is done by an ftrace probe on
sched_switch. This doesn't work well for the following events (with
letters representing timestamps):
A - sched switch probe called for task T switch out
B - __switch_to calltime is recorded
C - sched_switch probe called for task T switch in
D - __switch_to rettime is recorded

If C - A > D - B, then we end up over compensating for the time spent in
__switch_to giving rise to negative times in the trace output.

On x86, __switch_to is not traced if function graph tracer is enabled.
Do the same for arm64 as well.

Cc: Todd Kjos <tkjos@google.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Joel Fernandes <joelaf@google.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
This commit is contained in:
Joel Fernandes 2016-12-21 14:44:46 -08:00 committed by Will Deacon
parent a121103c92
commit 8f4b326d66
1 changed files with 1 additions and 1 deletions
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2
arch/arm64/kernel/process.c
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@ -339,7 +339,7 @@ static void entry_task_switch(struct task_struct *next)
/*
* Thread switching.
*/
struct task_struct *__switch_to(struct task_struct *prev,
__notrace_funcgraph struct task_struct *__switch_to(struct task_struct *prev,
struct task_struct *next)
{
struct task_struct *last;