On Thu, Jun 11, 2015 at 10:41:02PM +0800, Huang Rui wrote:
> MWAITX can enable a timer and a corresponding timer value specified in SW
> P0 clocks. The SW P0 frequency is the same with TSC. The timer provides an
> upper bound on how long the instruction waits before exiting.
>
> The implementation of delay function in kernel can lerverage the timer of
> MWAITX. This patch provides a new method (delay_mwaitx) to measure delay
> time.
>
> Suggested-by: Andy Lutomirski <[email protected]>
> Suggested-by: Borislav Petkov <[email protected]>
> Suggested-by: Peter Zijlstra <[email protected]>
> Signed-off-by: Huang Rui <[email protected]>
> ---
> arch/x86/include/asm/mwait.h | 11 +++++++++++
> arch/x86/lib/delay.c | 41 ++++++++++++++++++++++++++++++++++++++++-
> 2 files changed, 51 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/include/asm/mwait.h b/arch/x86/include/asm/mwait.h
> index 1fbc89d..9c8cccd 100644
> --- a/arch/x86/include/asm/mwait.h
> +++ b/arch/x86/include/asm/mwait.h
> @@ -14,6 +14,8 @@
> #define CPUID5_ECX_INTERRUPT_BREAK 0x2
>
> #define MWAIT_ECX_INTERRUPT_BREAK 0x1
> +#define MWAITX_ECX_TIMER_ENABLE BIT(1)
> +#define MWAITX_MAX_LOOPS ((u32)-1)
>
> static inline void __monitor(const void *eax, unsigned long ecx,
> unsigned long edx)
> @@ -104,4 +106,13 @@ static inline void mwait_idle_with_hints(unsigned long
> eax, unsigned long ecx)
> current_clr_polling();
> }
>
> +static inline void mwaitx(unsigned long eax, unsigned long loops,
> + bool enable)
> +{
> + if (enable)
> + __mwaitx(eax, loops, MWAITX_ECX_TIMER_ENABLE);
> + else
> + __mwaitx(eax, 0, 0);
> +}
> +
> #endif /* _ASM_X86_MWAIT_H */
> diff --git a/arch/x86/lib/delay.c b/arch/x86/lib/delay.c
> index 39d6a3d..9daf94a 100644
> --- a/arch/x86/lib/delay.c
> +++ b/arch/x86/lib/delay.c
> @@ -20,6 +20,7 @@
> #include <asm/processor.h>
> #include <asm/delay.h>
> #include <asm/timer.h>
> +#include <asm/mwait.h>
>
> #ifdef CONFIG_SMP
> # include <asm/smp.h>
> @@ -87,6 +88,41 @@ static void delay_tsc(unsigned long __loops)
> }
>
> /*
> + * On AMD platforms mwaitx has a configurable 32-bit timer, that counts
> + * with TSC frequency. And the input value is the loop of the counter, it
> + * will exit with the timer expired.
> + */
> +static void delay_mwaitx(unsigned long __loops)
> +{
> + u32 end, start, delay, addr, loops = __loops;
> +
> + rdtsc_barrier();
> + rdtscl(start);
> +
> + for (;;) {
> + delay = min(MWAITX_MAX_LOOPS, loops);
> +
> + __monitorx(&addr, 0, 0);
> + /*
> + * AMD, like Intel, supports the EAX hint and EAX=0xf
> + * means, do not enter any deep C-state and we use it
> + * here in delay() to minimize wakeup latency.
> + */
> + mwaitx(0xf, delay, true);
> +
> + rdtsc_barrier();
> + rdtscl(end);
> +
> + if (loops <= end - start)
> + break;
> +
> + loops -= end - start;
> +
> + start = end;
> + }
> +}
> +
> +/*
> * Since we calibrate only once at boot, this
> * function should be set once at boot and not changed
> */
> @@ -108,7 +144,10 @@ int read_current_timer(unsigned long *timer_val)
>
> void __delay(unsigned long loops)
> {
> - delay_fn(loops);
> + if (!static_cpu_has_safe(X86_FEATURE_MWAITT))
Actually, as Thomas suggested, you don't need that static_cpu_has_safe()
thing either. You can change use_tsc_delay() to do this:
void use_tsc_delay(void)
{
if (delay_fn == delay_loop)
delay_fn = delay_tsc;
}
and then add:
void use_mwaitx_delay(void)
{
delay_fn = delay_mwaitx;
}
and in cpu/amd.c:init_amd() do:
if (static_cpu_has_safe(X86_FEATURE_MWAITT))
use_mwaitx_delay();
Something like that, at least. tglx might have a better idea though.
--
Regards/Gruss,
Boris.
ECO tip #101: Trim your mails when you reply.
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