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x86/delay: Introduce TPAUSE delay

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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.

TPAUSE offers a choice of two lower power states:
 1. Light-weight power/performance optimized state C0.1
 2. Improved power/performance optimized state C0.2

This way, it can save power with low wake-up latency in comparison to
spinloop based delay. The selection between the two is governed by the
input register.

TPAUSE is available on processors with X86_FEATURE_WAITPKG.

Co-developed-by: Fenghua Yu <fenghua.yu@intel.com>
Signed-off-by: Fenghua Yu <fenghua.yu@intel.com>
Signed-off-by: Kyung Min Park <kyung.min.park@intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Tony Luck <tony.luck@intel.com>
Link: https://lkml.kernel.org/r/1587757076-30337-4-git-send-email-kyung.min.park@intel.com
This commit is contained in:
Kyung Min Park
2020-04-24 12:37:56 -07:00
committed by Thomas Gleixner
parent 46f90c7aad
commit cec5f268cd
5 changed files with 57 additions and 0 deletions
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27
arch/x86/lib/delay.c
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@@ -96,6 +96,27 @@ static void delay_tsc(u64 cycles)
preempt_enable();
}
/*
* On Intel the TPAUSE instruction waits until any of:
* 1) the TSC counter exceeds the value provided in EDX:EAX
* 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;
u32 eax, edx;
eax = lower_32_bits(until);
edx = upper_32_bits(until);
/*
* Hard code the deeper (C0.2) sleep state because exit latency is
* small compared to the "microseconds" that usleep() will delay.
*/
__tpause(TPAUSE_C02_STATE, edx, eax);
}
/*
* On some AMD platforms, MWAITX has a configurable 32-bit timer, that
* counts with TSC frequency. The input value is the number of TSC cycles
@@ -156,6 +177,12 @@ void __init use_tsc_delay(void)
delay_fn = delay_tsc;
}
void __init use_tpause_delay(void)
{
delay_halt_fn = delay_halt_tpause;
delay_fn = delay_halt;
}
void use_mwaitx_delay(void)
{
delay_halt_fn = delay_halt_mwaitx;