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Index: lib/libc/x86/sys/__vdso_gettc.c
===================================================================
--- lib/libc/x86/sys/__vdso_gettc.c
+++ lib/libc/x86/sys/__vdso_gettc.c
@@ -52,57 +52,108 @@
#endif
#include "libc_private.h"
+static enum LMB {
+ LMB_UNKNOWN,
+ LMB_NONE,
+ LMB_MFENCE,
+ LMB_LFENCE
+} lfence_works = LMB_UNKNOWN;
+
+static void
+cpuidp(u_int leaf, u_int p[4])
+{
+
+ __asm __volatile(
+#if defined(__i386__)
+ " pushl %%ebx\n"
+#endif
+ " cpuid\n"
+#if defined(__i386__)
+ " movl %%ebx,%1\n"
+ " popl %%ebx"
+#endif
+ : "=a" (p[0]),
+#if defined(__i386__)
+ "=r" (p[1]),
+#elif defined(__amd64__)
+ "=b" (p[1]),
+#else
+#error "Arch"
+#endif
+ "=c" (p[2]), "=d" (p[3])
+ : "0" (leaf));
+}
+
+static enum LMB
+select_lmb(void)
+{
+ u_int p[4];
+ static const char intel_id[] = "GenuntelineI";
+
+ cpuidp(0, p);
+ return (memcmp(p + 1, intel_id, sizeof(intel_id) - 1) == 0 ?
+ LMB_LFENCE : LMB_MFENCE);
+}
+
static void
-lfence_mb(void)
+init_fence(void)
{
#if defined(__i386__)
- static int lfence_works = -1;
u_int cpuid_supported, p[4];
- if (lfence_works == -1) {
- __asm __volatile(
- " pushfl\n"
- " popl %%eax\n"
- " movl %%eax,%%ecx\n"
- " xorl $0x200000,%%eax\n"
- " pushl %%eax\n"
- " popfl\n"
- " pushfl\n"
- " popl %%eax\n"
- " xorl %%eax,%%ecx\n"
- " je 1f\n"
- " movl $1,%0\n"
- " jmp 2f\n"
- "1: movl $0,%0\n"
- "2:\n"
- : "=r" (cpuid_supported) : : "eax", "ecx", "cc");
- if (cpuid_supported) {
- __asm __volatile(
- " pushl %%ebx\n"
- " cpuid\n"
- " movl %%ebx,%1\n"
- " popl %%ebx\n"
- : "=a" (p[0]), "=r" (p[1]), "=c" (p[2]), "=d" (p[3])
- : "0" (0x1));
- lfence_works = (p[3] & CPUID_SSE2) != 0;
- } else
- lfence_works = 0;
- }
- if (lfence_works == 1)
- lfence();
+ __asm __volatile(
+ " pushfl\n"
+ " popl %%eax\n"
+ " movl %%eax,%%ecx\n"
+ " xorl $0x200000,%%eax\n"
+ " pushl %%eax\n"
+ " popfl\n"
+ " pushfl\n"
+ " popl %%eax\n"
+ " xorl %%eax,%%ecx\n"
+ " je 1f\n"
+ " movl $1,%0\n"
+ " jmp 2f\n"
+ "1: movl $0,%0\n"
+ "2:\n"
+ : "=r" (cpuid_supported) : : "eax", "ecx", "cc");
+ if (cpuid_supported) {
+ cpuidp(0x1, p);
+ if ((p[3] & CPUID_SSE2) != 0)
+ lfence_works = select_lmb();
+ } else
+ lfence_works = LMB_NONE;
#elif defined(__amd64__)
- lfence();
+ lfence_works = select_lmb();
#else
-#error "arch"
+#error "Arch"
#endif
}
+static void
+rdtsc_mb(void)
+{
+
+again:
+ if (__predict_true(lfence_works == LMB_LFENCE)) {
+ lfence();
+ return;
+ } else if (lfence_works == LMB_MFENCE) {
+ mfence();
+ return;
+ } else if (lfence_works == LMB_NONE) {
+ return;
+ }
+ init_fence();
+ goto again;
+}
+
static u_int
__vdso_gettc_rdtsc_low(const struct vdso_timehands *th)
{
u_int rv;
- lfence_mb();
+ rdtsc_mb();
__asm __volatile("rdtsc; shrd %%cl, %%edx, %0"
: "=a" (rv) : "c" (th->th_x86_shift) : "edx");
return (rv);
@@ -112,7 +163,7 @@
__vdso_rdtsc32(void)
{
- lfence_mb();
+ rdtsc_mb();
return (rdtsc32());
}
@@ -212,7 +263,7 @@
scale = tsc_ref->tsc_scale;
ofs = tsc_ref->tsc_ofs;
- lfence_mb();
+ rdtsc_mb();
tsc = rdtsc();
/* ret = ((tsc * scale) >> 64) + ofs */

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