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| author |   Joel Fernandes <joelaf@google.com> | 2016-12-21 14:44:46 -0800 |
|---|---|---|
| committer |   Will Deacon <will.deacon@arm.com> | 2017-01-10 11:05:08 +0000 |
| commit | 8f4b326d663b92e1c2a53a6857bef42e91aea5a6 (patch) | |
| tree | f193952a90f4cd415a80a66e36069c1708245270 /arch/arm64/kernel/armv8_deprecated.c | |
| parent | Linux 4.10-rc3 (diff) | |
| download | linux-dev-8f4b326d663b92e1c2a53a6857bef42e91aea5a6.tar.xz linux-dev-8f4b326d663b92e1c2a53a6857bef42e91aea5a6.zip | |
arm64: Don't trace __switch_to if function graph tracer is enabled
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>
Diffstat (limited to 'arch/arm64/kernel/armv8_deprecated.c')
0 files changed, 0 insertions, 0 deletions