c5bcb5635a
RDTSCP is already synchronous and doesn't need an explicit CPUID. This is a little faster and more importantly avoids VMEXITs on Hypervisors. Original patch from Joerg Roedel, but reworked by AK Also includes miscompilation fix by Eric Biederman Cc: "Joerg Roedel" <joerg.roedel@amd.com> Signed-off-by: Andi Kleen <ak@suse.de>
73 lines
1.5 KiB
C
73 lines
1.5 KiB
C
/*
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* linux/include/asm-i386/tsc.h
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*
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* i386 TSC related functions
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*/
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#ifndef _ASM_i386_TSC_H
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#define _ASM_i386_TSC_H
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#include <asm/processor.h>
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/*
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* Standard way to access the cycle counter.
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*/
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typedef unsigned long long cycles_t;
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extern unsigned int cpu_khz;
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extern unsigned int tsc_khz;
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static inline cycles_t get_cycles(void)
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{
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unsigned long long ret = 0;
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#ifndef CONFIG_X86_TSC
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if (!cpu_has_tsc)
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return 0;
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#endif
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#if defined(CONFIG_X86_GENERIC) || defined(CONFIG_X86_TSC)
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rdtscll(ret);
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#endif
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return ret;
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}
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/* Like get_cycles, but make sure the CPU is synchronized. */
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static __always_inline cycles_t get_cycles_sync(void)
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{
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unsigned long long ret;
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unsigned eax;
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/*
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* Use RDTSCP if possible; it is guaranteed to be synchronous
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* and doesn't cause a VMEXIT on Hypervisors
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*/
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alternative_io(ASM_NOP3, ".byte 0x0f,0x01,0xf9", X86_FEATURE_RDTSCP,
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"=A" (ret), "0" (0ULL) : "ecx", "memory");
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if (ret)
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return ret;
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/*
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* Don't do an additional sync on CPUs where we know
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* RDTSC is already synchronous:
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*/
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alternative_io("cpuid", ASM_NOP2, X86_FEATURE_SYNC_RDTSC,
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"=a" (eax), "0" (1) : "ebx","ecx","edx","memory");
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rdtscll(ret);
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return ret;
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}
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extern void tsc_init(void);
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extern void mark_tsc_unstable(char *reason);
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extern int unsynchronized_tsc(void);
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extern void init_tsc_clocksource(void);
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/*
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* Boot-time check whether the TSCs are synchronized across
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* all CPUs/cores:
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*/
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extern void check_tsc_sync_source(int cpu);
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extern void check_tsc_sync_target(void);
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#endif
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