linux-kernel - [for-next][PATCH] tracing: Remove obsolete PREEMPTIRQ

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Message-ID: <20200608143133.0e72efde@oasis.local.home>
Date:   Mon, 8 Jun 2020 14:31:33 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     LKML <linux-kernel@...r.kernel.org>
Cc:     Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mel Gorman <mgorman@...hsingularity.net>
Subject: [for-next][PATCH] tracing: Remove obsolete PREEMPTIRQ_EVENTS
 kconfig option

  git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace.git
for-next

Head SHA1: 388d8bdb87e01bcea6d0b2bf797b5f6d7b2401fb


Mel Gorman (1):
      tracing: Remove obsolete PREEMPTIRQ_EVENTS kconfig option

----
 kernel/trace/Kconfig | 9 ---------
 1 file changed, 9 deletions(-)
---------------------------
commit 388d8bdb87e01bcea6d0b2bf797b5f6d7b2401fb
Author: Mel Gorman <mgorman@...hsingularity.net>
Date:   Thu Apr 9 11:40:34 2020 +0100

    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/20200409104034.GJ3818@techsingularity.net
    
    Signed-off-by: Mel Gorman <mgorman@...hsingularity.net>
    Signed-off-by: Steven Rostedt (VMware) <rostedt@...dmis.org>

diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
index 75407d5dc83a..0c82ac2c5688 100644
--- 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