3 files changed, 23 insertions, 0 deletions

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 8dd7248508a9..ed05a4a0d242 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -2435,6 +2435,10 @@ and is between 256 and 4096 characters. It is defined in the file
                         disables clocksource verification at runtime.
                         Used to enable high-resolution timer mode on older
                         hardware, and in virtualized environment.
+                        [x86] noirqtime: Do not use TSC to do irq accounting.
+                        Used to run time disable IRQ_TIME_ACCOUNTING on any
+                        platforms where RDTSC is slow and this accounting
+                        can add overhead.
 
         turbografx.map[2|3]=    [HW,JOY]
                         TurboGraFX parallel port interface
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index cea0cd9a316f..f4c70c246ffe 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -795,6 +795,17 @@ config SCHED_MC
           making when dealing with multi-core CPU chips at a cost of slightly
           increased overhead in some places. If unsure say N here.
 
+config IRQ_TIME_ACCOUNTING
+        bool "Fine granularity task level IRQ time accounting"
+        default n
+        ---help---
+          Select this option to enable fine granularity task irq time
+          accounting. This is done by reading a timestamp on each
+          transitions between softirq and hardirq state, so there can be a
+          small performance impact.
+
+          If in doubt, say N here.
+
 source "kernel/Kconfig.preempt"
 
 config X86_UP_APIC
diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index 26a863a9c2a8..a1c2cd768538 100644
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -104,10 +104,14 @@ int __init notsc_setup(char *str)
 
 __setup("notsc", notsc_setup);
 
+static int no_sched_irq_time;
+
 static int __init tsc_setup(char *str)
 {
         if (!strcmp(str, "reliable"))
                 tsc_clocksource_reliable = 1;
+        if (!strncmp(str, "noirqtime", 9))
+                no_sched_irq_time = 1;
         return 1;
 }
 
@@ -801,6 +805,7 @@ void mark_tsc_unstable(char *reason)
         if (!tsc_unstable) {
                 tsc_unstable = 1;
                 sched_clock_stable = 0;
+                disable_sched_clock_irqtime();
                 printk(KERN_INFO "Marking TSC unstable due to %s\n", reason);
                 /* Change only the rating, when not registered */
                 if (clocksource_tsc.mult)
@@ -987,6 +992,9 @@ void __init tsc_init(void)
         /* now allow native_sched_clock() to use rdtsc */
         tsc_disabled = 0;
 
+        if (!no_sched_irq_time)
+                enable_sched_clock_irqtime();
+
         lpj = ((u64)tsc_khz * 1000);
         do_div(lpj, HZ);
         lpj_fine = lpj;