On Fri, Oct 18, 2019 at 11:45:54AM +0800, Zhenzhong Duan wrote:
> If 'idle=nomwait' is specified or process matching what's in
> processor_idle_dmi_table, we should't use MWAIT at bootup stage before
> cpuidle driver loaded, even if it's preferred by default on Intel.
>
> Add a check so that HALT instruction is used in those cases.
The comment in idle_setup():
/*
* If the boot option of "idle=nomwait" is added,
* it means that mwait will be disabled for CPU C2/C3
* states. In such case it won't touch the variable
* of boot_option_idle_override.
*/
boot_option_idle_override = IDLE_NOMWAIT;
explicitly states this option is for C2+
> Signed-off-by: Zhenzhong Duan <zhenzhong.d...@oracle.com>
> Cc: Thomas Gleixner <t...@linutronix.de>
> Cc: Borislav Petkov <b...@alien8.de>
> Cc: Ingo Molnar <mi...@redhat.com>
> Cc: "H. Peter Anvin" <h...@zytor.com>
> Cc: Boris Ostrovsky <boris.ostrov...@oracle.com>
> ---
> arch/x86/kernel/process.c | 4 ++++
> 1 file changed, 4 insertions(+)
>
> diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
> index 5e94c43..37fc577 100644
> --- a/arch/x86/kernel/process.c
> +++ b/arch/x86/kernel/process.c
> @@ -667,6 +667,10 @@ static void amd_e400_idle(void)
> */
> static int prefer_mwait_c1_over_halt(const struct cpuinfo_x86 *c)
> {
> + /* Don't use MWAIT-C1 if explicitly requested */
> + if (boot_option_idle_override == IDLE_NOMWAIT)
> + return 0;
And this is very much about C1...
OTOH, "idle=halt" should be forcing HLT over MWAIT, so did you want to
write:
if (boot_option_idle_override == IDLE_HALT)
return 0;
instead?
