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Use MFENCE to serialize RDTSC on non-Intel CPUs.

Browse Source 
Kernel already used the stronger barrier instruction for AMDs, correct
the userspace fast gettimeofday() implementation as well.

Sponsored by:	The FreeBSD Foundation
MFC after:	2 weeks
Differential revision:	https://reviews.freebsd.org/D11728
This commit is contained in:
Konstantin Belousov 2017-07-27 08:37:07 +00:00
parent dd269a0bf4
commit 9a3083660d
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=321608
1 changed files with 89 additions and 38 deletions
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127
lib/libc/x86/sys/__vdso_gettc.c
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@ -52,57 +52,108 @@ __FBSDID("$FreeBSD$");
#endif
#include "libc_private.h"
static enum LMB {
LMB_UNKNOWN,
LMB_NONE,
LMB_MFENCE,
LMB_LFENCE
} lfence_works = LMB_UNKNOWN;
static void
lfence_mb(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
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 @@ static u_int
__vdso_rdtsc32(void)
{
lfence_mb();
rdtsc_mb();
return (rdtsc32());
}
@ -212,7 +263,7 @@ __vdso_hyperv_tsc(struct hyperv_reftsc *tsc_ref, u_int *tc)
scale = tsc_ref->tsc_scale;
ofs = tsc_ref->tsc_ofs;
lfence_mb();
rdtsc_mb();
tsc = rdtsc();
/* ret = ((tsc * scale) >> 64) + ofs */