Re: [RFC] Extend mwait idle to optimize away IPIs when possible

From: David Daney
Date: Mon Feb 06 2012 - 20:34:44 EST

On 02/06/2012 05:24 PM, H. Peter Anvin wrote:
On 02/06/2012 04:26 PM, David Daney wrote:
On 02/06/2012 12:42 PM, Venkatesh Pallipadi wrote:
index 5bed94e..6a56cb0 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -170,6 +170,11 @@ config GENERIC_TIME_VSYSCALL
default X86_64

+ bool
+ depends on X86_64
+ default X86_64

Can you get rid of this part...

def_bool y

diff --git a/arch/x86/kernel/acpi/cstate.c
index f50e7fb..340c4e9 100644
--- a/arch/x86/kernel/acpi/cstate.c
+++ b/arch/x86/kernel/acpi/cstate.c
@@ -161,6 +161,14 @@ EXPORT_SYMBOL_GPL(acpi_processor_ffh_cstate_probe);
void mwait_idle_with_hints(unsigned long ax, unsigned long cx)

... and change all of these to #ifdef CONFIG_64BIT

+ int oldval, cpu = smp_processor_id();

Why should this be 64-bit specific??

Well I don't know that part. The gist of my comment was to get rid of an unneeded new config variable.

If this works just as well for 32-bit, then by all means do it there too.

In any event, I think you want the kernel to automatically do it if the CPU is capable, and not have a manual config setting you have to fiddle with.

David Daney
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