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authorKonstantin Belousov <kib@FreeBSD.org>2016-08-17 09:52:09 +0000
committerKonstantin Belousov <kib@FreeBSD.org>2016-08-17 09:52:09 +0000
commit16808549465cce0799540b9c2d79c6a8cd40691a (patch)
treedb867e059f8908dd66ad19036e60c82be1dd7629 /lib/libc/x86/sys/__vdso_gettc.c
parent51c762d1722d1a39f355514e27b1de63a56c9f7f (diff)
downloadsrc-16808549465cce0799540b9c2d79c6a8cd40691a.tar.gz
src-16808549465cce0799540b9c2d79c6a8cd40691a.zip
Implement userspace gettimeofday(2) with HPET timecounter.
Right now, userspace (fast) gettimeofday(2) on x86 only works for RDTSC. For older machines, like Core2, where RDTSC is not C2/C3 invariant, and which fall to HPET hardware, this means that the call has both the penalty of the syscall and of the uncached hw behind the QPI or PCIe connection to the sought bridge. Nothing can me done against the access latency, but the syscall overhead can be removed. System already provides mappable /dev/hpetX devices, which gives straight access to the HPET registers page. Add yet another algorithm to the x86 'vdso' timehands. Libc is updated to handle both RDTSC and HPET. For HPET, the index of the hpet device to mmap is passed from kernel to userspace, index might be changed and libc invalidates its mapping as needed. Remove cpu_fill_vdso_timehands() KPI, instead require that timecounters which can be used from userspace, to provide tc_fill_vdso_timehands{,32}() methods. Merge i386 and amd64 libc/<arch>/sys/__vdso_gettc.c into one source file in the new libc/x86/sys location. __vdso_gettc() internal interface is changed to move timecounter algorithm detection into the MD code. Measurements show that RDTSC even with the syscall overhead is faster than userspace HPET access. But still, userspace HPET is three-four times faster than syscall HPET on several Core2 and SandyBridge machines. Tested by: Howard Su <howard0su@gmail.com> Sponsored by: The FreeBSD Foundation MFC after: 1 month Differential revision: https://reviews.freebsd.org/D7473
Notes
Notes: svn path=/head/; revision=304285
Diffstat (limited to 'lib/libc/x86/sys/__vdso_gettc.c')
-rw-r--r--lib/libc/x86/sys/__vdso_gettc.c179
1 files changed, 179 insertions, 0 deletions
diff --git a/lib/libc/x86/sys/__vdso_gettc.c b/lib/libc/x86/sys/__vdso_gettc.c
new file mode 100644
index 000000000000..743b3ad32779
--- /dev/null
+++ b/lib/libc/x86/sys/__vdso_gettc.c
@@ -0,0 +1,179 @@
+/*-
+ * Copyright (c) 2012 Konstantin Belousov <kib@FreeBSD.org>
+ * Copyright (c) 2016 The FreeBSD Foundation
+ * All rights reserved.
+ *
+ * Portions of this software were developed by Konstantin Belousov
+ * under sponsorship from the FreeBSD Foundation.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include <sys/cdefs.h>
+__FBSDID("$FreeBSD$");
+
+#include <sys/param.h>
+#include "namespace.h"
+#include <sys/elf.h>
+#include <sys/fcntl.h>
+#include <sys/mman.h>
+#include <sys/time.h>
+#include <sys/vdso.h>
+#include <errno.h>
+#include <string.h>
+#include <unistd.h>
+#include "un-namespace.h"
+#include <machine/cpufunc.h>
+#include <machine/specialreg.h>
+#include <dev/acpica/acpi_hpet.h>
+#include "libc_private.h"
+
+static void
+lfence_mb(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();
+#elif defined(__amd64__)
+ lfence();
+#else
+#error "arch"
+#endif
+}
+
+static u_int
+__vdso_gettc_rdtsc_low(const struct vdso_timehands *th)
+{
+ u_int rv;
+
+ lfence_mb();
+ __asm __volatile("rdtsc; shrd %%cl, %%edx, %0"
+ : "=a" (rv) : "c" (th->th_x86_shift) : "edx");
+ return (rv);
+}
+
+static u_int
+__vdso_rdtsc32(void)
+{
+
+ lfence_mb();
+ return (rdtsc32());
+}
+
+static char *hpet_dev_map = NULL;
+static uint32_t hpet_idx = 0xffffffff;
+
+static void
+__vdso_init_hpet(uint32_t u)
+{
+ static const char devprefix[] = "/dev/hpet";
+ char devname[64], *c, *c1, t;
+ int fd;
+
+ c1 = c = stpcpy(devname, devprefix);
+ u = hpet_idx;
+ do {
+ *c++ = u % 10 + '0';
+ u /= 10;
+ } while (u != 0);
+ *c = '\0';
+ for (c--; c1 != c; c1++, c--) {
+ t = *c1;
+ *c1 = *c;
+ *c = t;
+ }
+ fd = _open(devname, O_RDONLY);
+ if (fd == -1) {
+ hpet_dev_map = MAP_FAILED;
+ return;
+ }
+ if (hpet_dev_map != NULL && hpet_dev_map != MAP_FAILED)
+ munmap(hpet_dev_map, PAGE_SIZE);
+ hpet_dev_map = mmap(NULL, PAGE_SIZE, PROT_READ, MAP_SHARED, fd, 0);
+ _close(fd);
+}
+
+#pragma weak __vdso_gettc
+int
+__vdso_gettc(const struct vdso_timehands *th, u_int *tc)
+{
+ uint32_t tmp;
+
+ switch (th->th_algo) {
+ case VDSO_TH_ALGO_X86_TSC:
+ *tc = th->th_x86_shift > 0 ? __vdso_gettc_rdtsc_low(th) :
+ __vdso_rdtsc32();
+ return (0);
+ case VDSO_TH_ALGO_X86_HPET:
+ tmp = th->th_x86_hpet_idx;
+ if (hpet_dev_map == NULL || tmp != hpet_idx) {
+ hpet_idx = tmp;
+ __vdso_init_hpet(hpet_idx);
+ }
+ if (hpet_dev_map == MAP_FAILED)
+ return (ENOSYS);
+ *tc = *(volatile uint32_t *)(hpet_dev_map + HPET_MAIN_COUNTER);
+ return (0);
+ default:
+ return (ENOSYS);
+ }
+}
+
+#pragma weak __vdso_gettimekeep
+int
+__vdso_gettimekeep(struct vdso_timekeep **tk)
+{
+
+ return (_elf_aux_info(AT_TIMEKEEP, tk, sizeof(*tk)));
+}