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authorKyung Min Park <kyung.min.park@intel.com>2020-04-24 12:37:56 -0700
committerThomas Gleixner <tglx@linutronix.de>2020-05-07 16:06:20 +0200
commitcec5f268cd02d25d2d74807843d8ae0292fe0fb7 (patch)
tree917947f6e242b5f1c21e136cf3916dd09c3473ce /arch/x86/lib
parent46f90c7aad62be1af76588108c730d826308a801 (diff)
x86/delay: Introduce TPAUSE delay
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
Diffstat (limited to 'arch/x86/lib')
-rw-r--r--arch/x86/lib/delay.c27
1 files changed, 27 insertions, 0 deletions
diff --git a/arch/x86/lib/delay.c b/arch/x86/lib/delay.c
index fe91dc171cf8..65d15df6212d 100644
--- 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 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
* to wait. MWAITX will also exit when the timer expires.
@@ -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;