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Subject[PATCH] Add VDSO time function support for x86 32-bit kernel
Date
From: Stefani Seibold <stefani@seibold.net>

This small patch add the functions vdso_gettimeofday(), vdso_clock_gettime()
and vdso_time() support to the VDSO for x86 32-bit kernels.

The reason to do this was to get a fast reliable time stamp. Many developers
uses TSC to get a fast time time stamp, without knowing the pitfalls. VDSO
time functions a fast and reliable way, because the kernel knows the
best time source and the P- and C-state of the CPU.

The helper library to use the VDSO functions can be download at
http://http://seibold.net/vdso.c
The libary is very small, only 228 lines of code. Compile it with
gcc -Wall -O3 -fpic vdso.c -lrt -shared -o libvdso.so
and use it with LD_PRELOAD=<path>/libvdso.so

This kind of helper must be integrated into glibc, for x86 64-bit and
PowerPC it is already there.

Some benchmark results (all measurements are in nano seconds):

Intel(R) Celeron(TM) CPU 400MHz

Average time kernel call:
gettimeofday(): 1039
clock_gettime(): 1578
time(): 526
Average time VDSO call:
gettimeofday(): 378
clock_gettime(): 303
time(): 60

Celeron(R) Dual-Core CPU T3100 1.90GHz

Average time kernel call:
gettimeofday(): 209
clock_gettime(): 406
time(): 135
Average time VDSO call:
gettimeofday(): 51
clock_gettime(): 43
time(): 10

So you can see a performance increase between 4 and 13, depending on the
CPU and the function.

The patch is against kernel 3.7. Please apply if you like it.

Changelog:
25.11.2012 - first release and proof of concept for linux 3.4
11.12.2012 - Port to linux 3.7 and code cleanup
12.12.2012 - fixes suggested by Andy Lutomirski
- fixes suggested by John Stultz
- use call VDSO32_vsyscall instead of int 80
- code cleanup

Signed-off-by: Stefani Seibold <stefani@seibold.net>
---
arch/x86/Kconfig | 4 +-
arch/x86/include/asm/clocksource.h | 4 --
arch/x86/include/asm/fixmap.h | 3 +-
arch/x86/include/asm/vgtod.h | 1 +
arch/x86/include/asm/vvar.h | 7 +++
arch/x86/kernel/Makefile | 1 +
arch/x86/kernel/hpet.c | 9 ++--
arch/x86/kernel/setup.c | 2 +
arch/x86/kernel/tsc.c | 2 -
arch/x86/kernel/vmlinux.lds.S | 4 --
arch/x86/kernel/vsyscall_64.c | 49 ------------------
arch/x86/kernel/vsyscall_gtod.c | 93 +++++++++++++++++++++++++++++++++++
arch/x86/vdso/Makefile | 1 +
arch/x86/vdso/vclock_gettime.c | 25 +++++++++-
arch/x86/vdso/vdso32/vclock_gettime.c | 7 +++
arch/x86/vdso/vdso32/vdso32.lds.S | 5 ++
16 files changed, 151 insertions(+), 66 deletions(-)
create mode 100644 arch/x86/kernel/vsyscall_gtod.c
create mode 100644 arch/x86/vdso/vdso32/vclock_gettime.c

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 46c3bff..b8c2c74 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -100,9 +100,9 @@ config X86
select GENERIC_CMOS_UPDATE
select CLOCKSOURCE_WATCHDOG
select GENERIC_CLOCKEVENTS
- select ARCH_CLOCKSOURCE_DATA if X86_64
+ select ARCH_CLOCKSOURCE_DATA
select GENERIC_CLOCKEVENTS_BROADCAST if X86_64 || (X86_32 && X86_LOCAL_APIC)
- select GENERIC_TIME_VSYSCALL if X86_64
+ select GENERIC_TIME_VSYSCALL
select KTIME_SCALAR if X86_32
select GENERIC_STRNCPY_FROM_USER
select GENERIC_STRNLEN_USER
diff --git a/arch/x86/include/asm/clocksource.h b/arch/x86/include/asm/clocksource.h
index 0bdbbb3..67d68b9 100644
--- a/arch/x86/include/asm/clocksource.h
+++ b/arch/x86/include/asm/clocksource.h
@@ -3,8 +3,6 @@
#ifndef _ASM_X86_CLOCKSOURCE_H
#define _ASM_X86_CLOCKSOURCE_H

-#ifdef CONFIG_X86_64
-
#define VCLOCK_NONE 0 /* No vDSO clock available. */
#define VCLOCK_TSC 1 /* vDSO should use vread_tsc. */
#define VCLOCK_HPET 2 /* vDSO should use vread_hpet. */
@@ -13,6 +11,4 @@ struct arch_clocksource_data {
int vclock_mode;
};

-#endif /* CONFIG_X86_64 */
-
#endif /* _ASM_X86_CLOCKSOURCE_H */
diff --git a/arch/x86/include/asm/fixmap.h b/arch/x86/include/asm/fixmap.h
index 4da3c0c..b26e9e0 100644
--- a/arch/x86/include/asm/fixmap.h
+++ b/arch/x86/include/asm/fixmap.h
@@ -78,9 +78,10 @@ enum fixed_addresses {
VSYSCALL_LAST_PAGE,
VSYSCALL_FIRST_PAGE = VSYSCALL_LAST_PAGE
+ ((VSYSCALL_END-VSYSCALL_START) >> PAGE_SHIFT) - 1,
+#endif
VVAR_PAGE,
VSYSCALL_HPET,
-#endif
+
FIX_DBGP_BASE,
FIX_EARLYCON_MEM_BASE,
#ifdef CONFIG_PROVIDE_OHCI1394_DMA_INIT
diff --git a/arch/x86/include/asm/vgtod.h b/arch/x86/include/asm/vgtod.h
index 46e24d3..eb87b53 100644
--- a/arch/x86/include/asm/vgtod.h
+++ b/arch/x86/include/asm/vgtod.h
@@ -27,4 +27,5 @@ struct vsyscall_gtod_data {
};
extern struct vsyscall_gtod_data vsyscall_gtod_data;

+extern void map_vgtod(void);
#endif /* _ASM_X86_VGTOD_H */
diff --git a/arch/x86/include/asm/vvar.h b/arch/x86/include/asm/vvar.h
index de656ac..6f71098 100644
--- a/arch/x86/include/asm/vvar.h
+++ b/arch/x86/include/asm/vvar.h
@@ -17,7 +17,11 @@
*/

/* Base address of vvars. This is not ABI. */
+#ifdef CONFIG_X86_64
#define VVAR_ADDRESS (-10*1024*1024 - 4096)
+#else
+#define VVAR_ADDRESS 0xffffd000
+#endif

#if defined(__VVAR_KERNEL_LDS)

@@ -46,5 +50,8 @@
DECLARE_VVAR(0, volatile unsigned long, jiffies)
DECLARE_VVAR(16, int, vgetcpu_mode)
DECLARE_VVAR(128, struct vsyscall_gtod_data, vsyscall_gtod_data)
+#ifdef CONFIG_X86_32
+DECLARE_VVAR(512, const void __iomem *, vsyscall_hpet)
+#endif

#undef DECLARE_VVAR
diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
index 91ce48f..298a0b1 100644
--- a/arch/x86/kernel/Makefile
+++ b/arch/x86/kernel/Makefile
@@ -26,6 +26,7 @@ obj-y += probe_roms.o
obj-$(CONFIG_X86_32) += i386_ksyms_32.o
obj-$(CONFIG_X86_64) += sys_x86_64.o x8664_ksyms_64.o
obj-y += syscall_$(BITS).o
+obj-y += vsyscall_gtod.o
obj-$(CONFIG_X86_64) += vsyscall_64.o
obj-$(CONFIG_X86_64) += vsyscall_emu_64.o
obj-y += bootflag.o e820.o
diff --git a/arch/x86/kernel/hpet.c b/arch/x86/kernel/hpet.c
index 1460a5d..38887ca 100644
--- a/arch/x86/kernel/hpet.c
+++ b/arch/x86/kernel/hpet.c
@@ -69,13 +69,18 @@ static inline void hpet_writel(unsigned int d, unsigned int a)

#ifdef CONFIG_X86_64
#include <asm/pgtable.h>
+#else
+#include <asm/vvar.h>
+
+DEFINE_VVAR(const void __iomem *, vsyscall_hpet);
#endif

static inline void hpet_set_mapping(void)
{
hpet_virt_address = ioremap_nocache(hpet_address, HPET_MMAP_SIZE);
-#ifdef CONFIG_X86_64
__set_fixmap(VSYSCALL_HPET, hpet_address, PAGE_KERNEL_VVAR_NOCACHE);
+#ifdef CONFIG_X86_32
+ vsyscall_hpet = (const void __iomem *)fix_to_virt(VSYSCALL_HPET);
#endif
}

@@ -752,9 +757,7 @@ static struct clocksource clocksource_hpet = {
.mask = HPET_MASK,
.flags = CLOCK_SOURCE_IS_CONTINUOUS,
.resume = hpet_resume_counter,
-#ifdef CONFIG_X86_64
.archdata = { .vclock_mode = VCLOCK_HPET },
-#endif
};

static int hpet_clocksource_register(void)
diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
index ca45696..c2f6bbb 100644
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -114,6 +114,7 @@
#include <asm/mce.h>
#include <asm/alternative.h>
#include <asm/prom.h>
+#include <asm/vgtod.h>

/*
* end_pfn only includes RAM, while max_pfn_mapped includes all e820 entries.
@@ -997,6 +998,7 @@ void __init setup_arch(char **cmdline_p)
#ifdef CONFIG_X86_64
map_vsyscall();
#endif
+ map_vgtod();

generic_apic_probe();

diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index cfa5d4f..078cc9a 100644
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -772,9 +772,7 @@ static struct clocksource clocksource_tsc = {
.mask = CLOCKSOURCE_MASK(64),
.flags = CLOCK_SOURCE_IS_CONTINUOUS |
CLOCK_SOURCE_MUST_VERIFY,
-#ifdef CONFIG_X86_64
.archdata = { .vclock_mode = VCLOCK_TSC },
-#endif
};

void mark_tsc_unstable(char *reason)
diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
index 22a1530..31a0cdd 100644
--- a/arch/x86/kernel/vmlinux.lds.S
+++ b/arch/x86/kernel/vmlinux.lds.S
@@ -151,8 +151,6 @@ SECTIONS
_edata = .;
} :data

-#ifdef CONFIG_X86_64
-
. = ALIGN(PAGE_SIZE);
__vvar_page = .;

@@ -173,8 +171,6 @@ SECTIONS

. = ALIGN(__vvar_page + PAGE_SIZE, PAGE_SIZE);

-#endif /* CONFIG_X86_64 */
-
/* Init code and data - will be freed after init */
. = ALIGN(PAGE_SIZE);
.init.begin : AT(ADDR(.init.begin) - LOAD_OFFSET) {
diff --git a/arch/x86/kernel/vsyscall_64.c b/arch/x86/kernel/vsyscall_64.c
index 3a3e8c9..dfc9727 100644
--- a/arch/x86/kernel/vsyscall_64.c
+++ b/arch/x86/kernel/vsyscall_64.c
@@ -54,7 +54,6 @@
#include "vsyscall_trace.h"

DEFINE_VVAR(int, vgetcpu_mode);
-DEFINE_VVAR(struct vsyscall_gtod_data, vsyscall_gtod_data);

static enum { EMULATE, NATIVE, NONE } vsyscall_mode = EMULATE;

@@ -77,48 +76,6 @@ static int __init vsyscall_setup(char *str)
}
early_param("vsyscall", vsyscall_setup);

-void update_vsyscall_tz(void)
-{
- vsyscall_gtod_data.sys_tz = sys_tz;
-}
-
-void update_vsyscall(struct timekeeper *tk)
-{
- struct vsyscall_gtod_data *vdata = &vsyscall_gtod_data;
-
- write_seqcount_begin(&vdata->seq);
-
- /* copy vsyscall data */
- vdata->clock.vclock_mode = tk->clock->archdata.vclock_mode;
- vdata->clock.cycle_last = tk->clock->cycle_last;
- vdata->clock.mask = tk->clock->mask;
- vdata->clock.mult = tk->mult;
- vdata->clock.shift = tk->shift;
-
- vdata->wall_time_sec = tk->xtime_sec;
- vdata->wall_time_snsec = tk->xtime_nsec;
-
- vdata->monotonic_time_sec = tk->xtime_sec
- + tk->wall_to_monotonic.tv_sec;
- vdata->monotonic_time_snsec = tk->xtime_nsec
- + (tk->wall_to_monotonic.tv_nsec
- << tk->shift);
- while (vdata->monotonic_time_snsec >=
- (((u64)NSEC_PER_SEC) << tk->shift)) {
- vdata->monotonic_time_snsec -=
- ((u64)NSEC_PER_SEC) << tk->shift;
- vdata->monotonic_time_sec++;
- }
-
- vdata->wall_time_coarse.tv_sec = tk->xtime_sec;
- vdata->wall_time_coarse.tv_nsec = (long)(tk->xtime_nsec >> tk->shift);
-
- vdata->monotonic_time_coarse = timespec_add(vdata->wall_time_coarse,
- tk->wall_to_monotonic);
-
- write_seqcount_end(&vdata->seq);
-}
-
static void warn_bad_vsyscall(const char *level, struct pt_regs *regs,
const char *message)
{
@@ -366,8 +323,6 @@ void __init map_vsyscall(void)
{
extern char __vsyscall_page;
unsigned long physaddr_vsyscall = __pa_symbol(&__vsyscall_page);
- extern char __vvar_page;
- unsigned long physaddr_vvar_page = __pa_symbol(&__vvar_page);

__set_fixmap(VSYSCALL_FIRST_PAGE, physaddr_vsyscall,
vsyscall_mode == NATIVE
@@ -375,10 +330,6 @@ void __init map_vsyscall(void)
: PAGE_KERNEL_VVAR);
BUILD_BUG_ON((unsigned long)__fix_to_virt(VSYSCALL_FIRST_PAGE) !=
(unsigned long)VSYSCALL_START);
-
- __set_fixmap(VVAR_PAGE, physaddr_vvar_page, PAGE_KERNEL_VVAR);
- BUILD_BUG_ON((unsigned long)__fix_to_virt(VVAR_PAGE) !=
- (unsigned long)VVAR_ADDRESS);
}

static int __init vsyscall_init(void)
diff --git a/arch/x86/kernel/vsyscall_gtod.c b/arch/x86/kernel/vsyscall_gtod.c
new file mode 100644
index 0000000..9b96488
--- /dev/null
+++ b/arch/x86/kernel/vsyscall_gtod.c
@@ -0,0 +1,93 @@
+/*
+ * Copyright (C) 2001 Andrea Arcangeli <andrea@suse.de> SuSE
+ * Copyright 2003 Andi Kleen, SuSE Labs.
+ *
+ * Modified for x86 32 bit architecture by
+ * Stefani Seibold <stefani@seibold.net>
+ *
+ * Thanks to hpa@transmeta.com for some useful hint.
+ * Special thanks to Ingo Molnar for his early experience with
+ * a different vsyscall implementation for Linux/IA32 and for the name.
+ *
+ */
+
+#include <linux/time.h>
+#include <linux/init.h>
+#include <linux/kernel.h>
+#include <linux/timer.h>
+#include <linux/seqlock.h>
+#include <linux/jiffies.h>
+#include <linux/sysctl.h>
+#include <linux/topology.h>
+#include <linux/timekeeper_internal.h>
+#include <linux/ratelimit.h>
+
+#include <asm/vsyscall.h>
+#include <asm/pgtable.h>
+#include <asm/page.h>
+#include <asm/unistd.h>
+#include <asm/fixmap.h>
+#include <asm/errno.h>
+#include <asm/io.h>
+#include <asm/segment.h>
+#include <asm/desc.h>
+#include <asm/topology.h>
+#include <asm/vgtod.h>
+#include <asm/traps.h>
+
+DEFINE_VVAR(struct vsyscall_gtod_data, vsyscall_gtod_data);
+
+void update_vsyscall_tz(void)
+{
+ vsyscall_gtod_data.sys_tz = sys_tz;
+}
+
+void update_vsyscall(struct timekeeper *tk)
+{
+ struct vsyscall_gtod_data *vdata = &vsyscall_gtod_data;
+
+ write_seqcount_begin(&vdata->seq);
+
+ /* copy vsyscall data */
+ vdata->clock.vclock_mode = tk->clock->archdata.vclock_mode;
+ vdata->clock.cycle_last = tk->clock->cycle_last;
+ vdata->clock.mask = tk->clock->mask;
+ vdata->clock.mult = tk->mult;
+ vdata->clock.shift = tk->shift;
+
+ vdata->wall_time_sec = tk->xtime_sec;
+ vdata->wall_time_snsec = tk->xtime_nsec;
+
+ vdata->monotonic_time_sec = tk->xtime_sec
+ + tk->wall_to_monotonic.tv_sec;
+ vdata->monotonic_time_snsec = tk->xtime_nsec
+ + (tk->wall_to_monotonic.tv_nsec
+ << tk->shift);
+ while (vdata->monotonic_time_snsec >=
+ (((u64)NSEC_PER_SEC) << tk->shift)) {
+ vdata->monotonic_time_snsec -=
+ ((u64)NSEC_PER_SEC) << tk->shift;
+ vdata->monotonic_time_sec++;
+ }
+
+ vdata->wall_time_coarse.tv_sec = tk->xtime_sec;
+ vdata->wall_time_coarse.tv_nsec = (long)(tk->xtime_nsec >> tk->shift);
+
+ vdata->monotonic_time_coarse = timespec_add(vdata->wall_time_coarse,
+ tk->wall_to_monotonic);
+
+ write_seqcount_end(&vdata->seq);
+}
+
+void __init map_vgtod(void)
+{
+ extern char __vvar_page;
+ unsigned long physaddr_vvar_page = __pa_symbol(&__vvar_page);
+
+ __set_fixmap(VVAR_PAGE, physaddr_vvar_page, PAGE_KERNEL_VVAR);
+#ifdef CONFIG_X86_64
+ BUILD_BUG_ON((unsigned long)__fix_to_virt(VVAR_PAGE) !=
+ (unsigned long)VVAR_ADDRESS);
+#endif
+}
+
diff --git a/arch/x86/vdso/Makefile b/arch/x86/vdso/Makefile
index fd14be1..959221b 100644
--- a/arch/x86/vdso/Makefile
+++ b/arch/x86/vdso/Makefile
@@ -147,6 +147,7 @@ $(vdso32-images:%=$(obj)/%.dbg): asflags-$(CONFIG_X86_64) += -m32

$(vdso32-images:%=$(obj)/%.dbg): $(obj)/vdso32-%.so.dbg: FORCE \
$(obj)/vdso32/vdso32.lds \
+ $(obj)/vdso32/vclock_gettime.o \
$(obj)/vdso32/note.o \
$(obj)/vdso32/%.o
$(call if_changed,vdso)
diff --git a/arch/x86/vdso/vclock_gettime.c b/arch/x86/vdso/vclock_gettime.c
index 4df6c37..3490e1c 100644
--- a/arch/x86/vdso/vclock_gettime.c
+++ b/arch/x86/vdso/vclock_gettime.c
@@ -57,6 +57,7 @@ notrace static cycle_t vread_tsc(void)
return last;
}

+#ifdef CONFIG_X86_64
static notrace cycle_t vread_hpet(void)
{
return readl((const void __iomem *)fix_to_virt(VSYSCALL_HPET) + 0xf0);
@@ -78,11 +79,33 @@ notrace static long vdso_fallback_gtod(struct timeval *tv, struct timezone *tz)
"0" (__NR_gettimeofday), "D" (tv), "S" (tz) : "memory");
return ret;
}
+#else
+static notrace cycle_t vread_hpet(void)
+{
+ return readl(VVAR(vsyscall_hpet) + HPET_COUNTER);
+}

+notrace static long vdso_fallback_gettime(long clock, struct timespec *ts)
+{
+ long ret;
+ asm("call VDSO32_vsyscall" : "=a" (ret) :
+ "a" (__NR_clock_gettime), "b" (clock), "c" (ts) : "memory");
+ return ret;
+}
+
+notrace static long vdso_fallback_gtod(struct timeval *tv, struct timezone *tz)
+{
+ long ret;
+
+ asm("call VDSO32_vsyscall" : "=a" (ret) :
+ "a" (__NR_gettimeofday), "b" (tv), "c" (tz) : "memory");
+ return ret;
+}
+#endif

notrace static inline u64 vgetsns(void)
{
- long v;
+ u64 v;
cycles_t cycles;
if (gtod->clock.vclock_mode == VCLOCK_TSC)
cycles = vread_tsc();
diff --git a/arch/x86/vdso/vdso32/vclock_gettime.c b/arch/x86/vdso/vdso32/vclock_gettime.c
new file mode 100644
index 0000000..c9a1909
--- /dev/null
+++ b/arch/x86/vdso/vdso32/vclock_gettime.c
@@ -0,0 +1,7 @@
+/*
+ * since vgtod layout differs between X86_64 and x86_32, it is not possible to
+ * provide a 32 bit vclock with a 64 bit kernel
+ */
+#ifdef CONFIG_X86_32
+#include "../vclock_gettime.c"
+#endif
diff --git a/arch/x86/vdso/vdso32/vdso32.lds.S b/arch/x86/vdso/vdso32/vdso32.lds.S
index 976124b..197d50f 100644
--- a/arch/x86/vdso/vdso32/vdso32.lds.S
+++ b/arch/x86/vdso/vdso32/vdso32.lds.S
@@ -24,6 +24,11 @@ VERSION
__kernel_vsyscall;
__kernel_sigreturn;
__kernel_rt_sigreturn;
+#ifdef CONFIG_X86_32
+ __vdso_clock_gettime;
+ __vdso_gettimeofday;
+ __vdso_time;
+#endif
local: *;
};
}
--
1.8.0


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