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authorSepherosa Ziehau <sephe@FreeBSD.org>2016-12-19 07:40:45 +0000
committerSepherosa Ziehau <sephe@FreeBSD.org>2016-12-19 07:40:45 +0000
commitfff5be0be3de457714cbe05854bc76ee0aff08a0 (patch)
tree114904e805c073b49ecebb24ec75ddc29d0d0640 /lib/libc/x86/sys/__vdso_gettc.c
parentd8303c114b429b409aaa1849d26e5aec89d1620a (diff)
downloadsrc-fff5be0be3de457714cbe05854bc76ee0aff08a0.tar.gz
src-fff5be0be3de457714cbe05854bc76ee0aff08a0.zip
hyperv: Implement userspace gettimeofday(2) with Hyper-V reference TSC
This 6 times gettimeofday performance, as measured by tools/tools/syscall_timing Reviewed by: kib MFC after: 1 week Sponsored by: Microsoft Differential Revision: https://reviews.freebsd.org/D8789
Notes
Notes: svn path=/head/; revision=310239
Diffstat (limited to 'lib/libc/x86/sys/__vdso_gettc.c')
-rw-r--r--lib/libc/x86/sys/__vdso_gettc.c73
1 files changed, 73 insertions, 0 deletions
diff --git a/lib/libc/x86/sys/__vdso_gettc.c b/lib/libc/x86/sys/__vdso_gettc.c
index 743b3ad32779..5097ad515650 100644
--- a/lib/libc/x86/sys/__vdso_gettc.c
+++ b/lib/libc/x86/sys/__vdso_gettc.c
@@ -45,6 +45,10 @@ __FBSDID("$FreeBSD$");
#include <machine/cpufunc.h>
#include <machine/specialreg.h>
#include <dev/acpica/acpi_hpet.h>
+#ifdef __amd64__
+#include <machine/atomic.h>
+#include <dev/hyperv/hyperv.h>
+#endif
#include "libc_private.h"
static void
@@ -144,6 +148,67 @@ __vdso_init_hpet(uint32_t u)
_close(fd);
}
+#ifdef __amd64__
+
+#define HYPERV_REFTSC_DEVPATH "/dev/" HYPERV_REFTSC_DEVNAME
+
+/*
+ * NOTE:
+ * We use 'NULL' for this variable to indicate that initialization
+ * is required. And if this variable is 'MAP_FAILED', then Hyper-V
+ * reference TSC can not be used, e.g. in misconfigured jail.
+ */
+static struct hyperv_reftsc *hyperv_ref_tsc;
+
+static void
+__vdso_init_hyperv_tsc(void)
+{
+ int fd;
+
+ fd = _open(HYPERV_REFTSC_DEVPATH, O_RDONLY);
+ if (fd < 0) {
+ /* Prevent the caller from re-entering. */
+ hyperv_ref_tsc = MAP_FAILED;
+ return;
+ }
+ hyperv_ref_tsc = mmap(NULL, sizeof(*hyperv_ref_tsc), PROT_READ,
+ MAP_SHARED, fd, 0);
+ _close(fd);
+}
+
+static int
+__vdso_hyperv_tsc(struct hyperv_reftsc *tsc_ref, u_int *tc)
+{
+ uint64_t disc, ret, tsc, scale;
+ uint32_t seq;
+ int64_t ofs;
+
+ while ((seq = atomic_load_acq_int(&tsc_ref->tsc_seq)) != 0) {
+ scale = tsc_ref->tsc_scale;
+ ofs = tsc_ref->tsc_ofs;
+
+ lfence_mb();
+ tsc = rdtsc();
+
+ /* ret = ((tsc * scale) >> 64) + ofs */
+ __asm__ __volatile__ ("mulq %3" :
+ "=d" (ret), "=a" (disc) :
+ "a" (tsc), "r" (scale));
+ ret += ofs;
+
+ atomic_thread_fence_acq();
+ if (tsc_ref->tsc_seq == seq) {
+ *tc = ret;
+ return (0);
+ }
+
+ /* Sequence changed; re-sync. */
+ }
+ return (ENOSYS);
+}
+
+#endif /* __amd64__ */
+
#pragma weak __vdso_gettc
int
__vdso_gettc(const struct vdso_timehands *th, u_int *tc)
@@ -165,6 +230,14 @@ __vdso_gettc(const struct vdso_timehands *th, u_int *tc)
return (ENOSYS);
*tc = *(volatile uint32_t *)(hpet_dev_map + HPET_MAIN_COUNTER);
return (0);
+#ifdef __amd64__
+ case VDSO_TH_ALGO_X86_HVTSC:
+ if (hyperv_ref_tsc == NULL)
+ __vdso_init_hyperv_tsc();
+ if (hyperv_ref_tsc == MAP_FAILED)
+ return (ENOSYS);
+ return (__vdso_hyperv_tsc(hyperv_ref_tsc, tc));
+#endif
default:
return (ENOSYS);
}