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tracing: Remove obsolete PREEMPTIRQ_EVENTS kconfig option 

The PREEMPTIRQ_EVENTS option is unused after commit c3bc8fd637 ("tracing:
Centralize preemptirq tracepoints and unify their usage"). Remove it.

Note that this option is hazardous as it stands. It enables TRACE_IRQFLAGS
event on non-preempt configurations without the irqsoff tracer enabled.
TRACE_IRQFLAGS as it stands incurs significant overhead on each IRQ
entry/exit. This is because trace_hardirqs_[on|off] does all the per-cpu
manipulations and NMI checks even if tracing is completely disabled for
some insane reason.  For example, netperf running UDP_STREAM on localhost
incurs a 4-6% performance penalty without any tracing if IRQFLAGS is
set. It can be put behind a static brach but even the function entry/exit
costs a little bit.

Link: https://lkml.kernel.org/r/20200409104034.GJ3818@techsingularity.net

Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
This commit is contained in:
Mel Gorman 2020-04-09 11:40:34 +01:00 committed by Steven Rostedt (VMware)
parent daceabf1b4
commit 388d8bdb87
1 changed files with 0 additions and 9 deletions
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9
kernel/trace/Kconfig
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@ -258,15 +258,6 @@ config TRACE_PREEMPT_TOGGLE
Enables hooks which will be called when preemption is first disabled,
and last enabled.
config PREEMPTIRQ_EVENTS
bool "Enable trace events for preempt and irq disable/enable"
select TRACE_IRQFLAGS
select TRACE_PREEMPT_TOGGLE if PREEMPTION
select GENERIC_TRACER
default n
help
Enable tracing of disable and enable events for preemption and irqs.
config IRQSOFF_TRACER
bool "Interrupts-off Latency Tracer"
default n