tracing: Remove obsolete PREEMPTIRQ_EVENTS kconfig option

The PREEMPTIRQ_EVENTS option is unused after commit c3bc8fd637a9 ("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/[email protected]
Signed-off-by: Mel Gorman <[email protected]>
Signed-off-by: Steven Rostedt (VMware) <[email protected]>

diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
index 75407d5dc83a4e17adc8482e0826b43be33c4c4e..0c82ac2c5688c09df4e9d403e3744cd9e494be9f 100644 (file)
--- a/kernel/trace/Kconfig
+++ b/kernel/trace/Kconfig
@@ -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