From: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
In drv_read(), check to see whether we can run the rdmsr() on the current
CPU. If so, do that. So smp_call_function_single() can avoid the IPI.
Arguably, cpumask_any() should do this.
Cc: Rusty Russell <rusty@xxxxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxx>
Cc: Venkatesh Pallipadi <venkatesh.pallipadi@xxxxxxxxx>
Cc: Len Brown <len.brown@xxxxxxxxx>
Cc: Zhao Yakui <yakui.zhao@xxxxxxxxx>
Cc: Dave Jones <davej@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Tested-by: Mike Galbraith <efault@xxxxxx>
Cc: "Zhang, Yanmin" <yanmin_zhang@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
arch/x86/kernel/cpu/cpufreq/acpi-cpufreq.c | 17 +++++++++++++++--
1 file changed, 15 insertions(+), 2 deletions(-)
diff -puN arch/x86/kernel/cpu/cpufreq/acpi-cpufreq.c~arch-x86-kernel-cpu-cpufreq-acpi-cpufreqc-avoid-cross-cpu-interrupts arch/x86/kernel/cpu/cpufreq/acpi-cpufreq.c
--- a/arch/x86/kernel/cpu/cpufreq/acpi-cpufreq.c~arch-x86-kernel-cpu-cpufreq-acpi-cpufreqc-avoid-cross-cpu-interrupts
+++ a/arch/x86/kernel/cpu/cpufreq/acpi-cpufreq.c
@@ -197,9 +197,22 @@ static void do_drv_write(void *_cmd)
static void drv_read(struct drv_cmd *cmd)
{
- cmd->val = 0;
+ int target_cpu; /* The CPU on which to perform thr rdmsr() */
+ int this_cpu;
+
+ /*
+ * If the current CPU is in cmd->mask then run the rdmsr() on this
+ * CPU to avoid the cross-cpu interrupt.
+ */
+ this_cpu = get_cpu();
+ if (cpu_isset(this_cpu, *(cmd->mask)))
+ target_cpu = this_cpu;
+ else
+ target_cpu = cpumask_any(cmd->mask);
- smp_call_function_single(cpumask_any(cmd->mask), do_drv_read, cmd, 1);
+ cmd->val = 0;
+ smp_call_function_single(target_cpu, do_drv_read, cmd, 1);
+ put_cpu();
}
static void drv_write(struct drv_cmd *cmd)
_
--
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