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SubjectRe: [PATCH v2 2/2] x86/delay: Introduce TPAUSE delay
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On Thu, 2020-03-19 at 21:13 -0700, Kyung Min Park wrote:
> TPAUSE instructs the processor to enter an implementation-dependent
> optimized state. The instruction execution wakes up when the time-stamp
> counter reaches or exceeds the implicit EDX:EAX 64-bit input value.
> The instruction execution also wakes up due to the expiration of
> the operating system time-limit or by an external interrupt
> or exceptions such as a debug exception or a machine check exception.
[]
> diff --git a/arch/x86/lib/delay.c b/arch/x86/lib/delay.c
[]
> @@ -97,6 +97,27 @@ static void delay_tsc(u64 cycles)
> }
>
> /*
> + * On Intel the TPAUSE instruction waits until any of:
> + * 1) the TSC counter exceeds the value provided in EAX:EDX
> + * 2) global timeout in IA32_UMWAIT_CONTROL is exceeded
> + * 3) an external interrupt occurs
> + */
> +static void delay_halt_tpause(u64 start, u64 cycles)
> +{
> + u64 until = start + cycles;
> + unsigned int eax, edx;
> +
> + eax = (unsigned int)(until & 0xffffffff);
> + edx = (unsigned int)(until >> 32);

trivia:

perhaps lower_32_bits and upper_32_bits


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