x86 vdso gettc: Add RDTSCP support
Detect and use RDTSCP if available, instead of fence+RDTSC. For AMD Zens+, use LFENCE+RDTSC instead of RDTSCP (or MFENCE;RDTSC previously). Reviewed by: gallatin, markj Tested by: pho MFC after: 1 week Sponsored by: The FreeBSD Foundation Differential Revision: https://reviews.freebsd.org/D27986
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@ -63,6 +63,16 @@ rdtsc_low(const struct vdso_timehands *th)
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return (rv);
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}
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static inline u_int
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rdtscp_low(const struct vdso_timehands *th)
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{
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u_int rv;
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__asm __volatile("rdtscp; movl %%edi,%%ecx; shrd %%cl, %%edx, %0"
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: "=a" (rv) : "D" (th->th_x86_shift) : "ecx", "edx");
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return (rv);
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}
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static u_int
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rdtsc_low_mb_lfence(const struct vdso_timehands *th)
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{
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@ -103,6 +113,12 @@ rdtsc32_mb_none(void)
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return (rdtsc32());
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}
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static u_int
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rdtscp32_(void)
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{
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return (rdtscp32());
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}
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struct tsc_selector_tag {
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u_int (*ts_rdtsc32)(void);
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u_int (*ts_rdtsc_low)(const struct vdso_timehands *);
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@ -121,6 +137,10 @@ static const struct tsc_selector_tag tsc_selector[] = {
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.ts_rdtsc32 = rdtsc32_mb_none,
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.ts_rdtsc_low = rdtsc_low_mb_none,
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},
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[3] = { /* RDTSCP */
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.ts_rdtsc32 = rdtscp32_,
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.ts_rdtsc_low = rdtscp_low,
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},
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};
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static int
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@ -144,6 +164,9 @@ tsc_selector_idx(u_int cpu_feature)
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do_cpuid(1, p);
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cpu_id = p[0];
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if (amd_cpu && CPUID_TO_FAMILY(cpu_id) >= 0x17)
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return (0);
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if (cpu_feature != 0) {
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do_cpuid(0x80000000, p);
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cpu_exthigh = p[0];
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@ -157,6 +180,8 @@ tsc_selector_idx(u_int cpu_feature)
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amd_feature = 0;
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}
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if ((amd_feature & AMDID_RDTSCP) != 0)
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return (3);
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if ((cpu_feature & CPUID_SSE2) == 0)
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return (2);
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return (amd_cpu ? 1 : 0);
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