bionic: add vdso time()
time() can be a hot call, and it currently uses __vdso_gettimeofday,
which is already pretty fast (~3 times faster than the syscall),
but with a __vdso_time call it is ~3 times even faster, in part
because __vdso_time does not require interlocking with updates,
and the read for just the seconds is atomic. __vdso_time is
always available, whereas __vdso_gettimeofday is gated on access
to the physical timers. arm improvement is compelling (x10),
x86 improvement is even more pronounced (x100).
[TL;DR]
w/vdso32 kernel patches, locked cores to MAX, little cores only.
BEFORE:
hikey960 vdso (aarch64):
----------------------------------------------------------------------
Benchmark Time CPU Iterations
----------------------------------------------------------------------
BM_time_clock_gettime 48 ns 48 ns 15414753
BM_time_clock_gettime_syscall 175 ns 175 ns 4062031
BM_time_clock_gettime_REALTIME 44 ns 44 ns 15897875
BM_time_clock_gettime_BOOTTIME 47 ns 47 ns 14307903
BM_time_clock_gettime_TAI 210 ns 210 ns 3341372
BM_time_clock_gettime_unsupported 100 ns 100 ns 7030649
BM_time_gettimeofday 47 ns 47 ns 14969643
BM_time_gettimeofday_syscall 163 ns 163 ns 4283542
BM_time_time 59 ns 59 ns 11815385
hikey960 vdso32 (aarch32):
----------------------------------------------------------------------
Benchmark Time CPU Iterations
----------------------------------------------------------------------
BM_time_clock_gettime 90 ns 90 ns 7572898
BM_time_clock_gettime_syscall 251 ns 251 ns 2763442
BM_time_clock_gettime_REALTIME 81 ns 80 ns 8699536
BM_time_clock_gettime_BOOTTIME 97 ns 97 ns 7256667
BM_time_clock_gettime_TAI 272 ns 272 ns 2570419
BM_time_clock_gettime_unsupported 160 ns 160 ns 4379819
BM_time_gettimeofday 73 ns 73 ns 9608922
BM_time_gettimeofday_syscall 200 ns 199 ns 3527957
BM_time_time 123 ns 123 ns 5651095
x86_64 (glibc):
--------------------------------------------------------------------
Benchmark Time CPU Iterations
--------------------------------------------------------------------
BM_time_clock_gettime 21 ns 21 ns 28873070
BM_time_clock_gettime_syscall 224 ns 224 ns 3095370
BM_time_clock_gettime_REALTIME 17 ns 17 ns 42083086
BM_time_clock_gettime_BOOTTIME 239 ns 239 ns 2924015
BM_time_clock_gettime_TAI 236 ns 236 ns 2961423
BM_time_clock_gettime_unsupported 221 ns 221 ns 3357696
BM_time_gettimeofday 22 ns 22 ns 27975154
BM_time_gettimeofday_syscall 238 ns 238 ns 2882032
BM_time_time 2 ns 2 ns 340354885
BM_time_time_syscall 207 ns 207 ns 3383073
imx7d_pico IOT nyc (w/arm,cpu-registers-not-fw-configured) (armv7a):
(virtual timers)
Benchmark Time(ns) CPU(ns) Iterations
------------------------------------------------------------------
BM_time_clock_gettime 20 477 1489362
BM_time_clock_gettime_syscall 20 487 1458333
BM_time_clock_gettime_REALTIME 19 464 1400000
BM_time_clock_gettime_BOOTTIME 29 700 1000000
BM_time_clock_gettime_TAI 29 690 1000000
BM_time_clock_gettime_unsupported 9 227 3043478
BM_time_gettimeofday 18 444 1555556
BM_time_gettimeofday_syscall 19 456 1555556
BM_time_time 21 497 1166667
imx7d_pico IOT nyc (wo/arm,cpu-registers-not-fw-configured) (armv7a):
(physical timers)
Benchmark Time(ns) CPU(ns) Iterations
------------------------------------------------------------------
BM_time_clock_gettime 6 144 4666667
BM_time_clock_gettime_syscall 20 486 1400000
BM_time_clock_gettime_REALTIME 6 136 5000000
BM_time_clock_gettime_BOOTTIME 6 153 4375000
BM_time_clock_gettime_TAI 31 760 1000000
BM_time_clock_gettime_unsupported 10 233 3043478
BM_time_gettimeofday 6 140 5000000
BM_time_gettimeofday_syscall 19 450 1555556
BM_time_time 9 203 3500000
AFTER:
hikey960 vdso (aarch64):
--------------------------------------------------------------------
Benchmark Time CPU Iterations
--------------------------------------------------------------------
BM_time_clock_gettime 48 ns 48 ns 15414753
BM_time_clock_gettime_syscall 175 ns 175 ns 4062031
BM_time_clock_gettime_REALTIME 44 ns 44 ns 15897875
BM_time_clock_gettime_BOOTTIME 47 ns 47 ns 14307903
BM_time_clock_gettime_TAI 210 ns 210 ns 3341372
BM_time_clock_gettime_unsupported 100 ns 100 ns 7030649
BM_time_gettimeofday 47 ns 47 ns 14975314
BM_time_gettimeofday_syscall 164 ns 164 ns 4278797
BM_time_time 16 ns 16 ns 42932165
hikey960 vdso32 (aarch32):
--------------------------------------------------------------------
Benchmark Time CPU Iterations
--------------------------------------------------------------------
BM_time_clock_gettime 90 ns 90 ns 7572898
BM_time_clock_gettime_syscall 251 ns 251 ns 2763442
BM_time_clock_gettime_REALTIME 81 ns 80 ns 8699536
BM_time_clock_gettime_BOOTTIME 97 ns 97 ns 7256667
BM_time_clock_gettime_TAI 272 ns 272 ns 2570419
BM_time_clock_gettime_unsupported 160 ns 160 ns 4379819
BM_time_gettimeofday 73 ns 73 ns 9596230
BM_time_gettimeofday_syscall 199 ns 199 ns 3575428
BM_time_time 35 ns 35 ns 19798801
imx7d_pico IOT nyc (w/arm,cpu-registers-not-fw-configured) (armv7a):
Benchmark Time(ns) CPU(ns) Iterations
------------------------------------------------------------------
BM_time_clock_gettime 20 477 1489362
BM_time_clock_gettime_syscall 20 487 1458333
BM_time_clock_gettime_REALTIME 19 464 1400000
BM_time_clock_gettime_BOOTTIME 29 700 1000000
BM_time_clock_gettime_TAI 29 690 1000000
BM_time_clock_gettime_unsupported 9 227 3043478
BM_time_gettimeofday 18 444 1555556
BM_time_gettimeofday_syscall 19 456 1555556
BM_time_time 2 50 11666667
imx7d_pico IOT nyc (wo/arm,cpu-registers-not-fw-configured) (armv7a):
Benchmark Time(ns) CPU(ns) Iterations
------------------------------------------------------------------
BM_time_clock_gettime 6 144 4666667
BM_time_clock_gettime_syscall 20 486 1400000
BM_time_clock_gettime_REALTIME 6 136 5000000
BM_time_clock_gettime_BOOTTIME 6 153 4375000
BM_time_clock_gettime_TAI 31 760 1000000
BM_time_clock_gettime_unsupported 10 233 3043478
BM_time_gettimeofday 6 140 5000000
BM_time_gettimeofday_syscall 19 450 1555556
BM_time_time 2 50 10000000
Test: bionic-unit-tests --gtest_filter=time.time
taskset F bionic-benchmarks --bionic_xml=vdso.xml \
--benchmark_filter='BM_time_(time*|clock_gettime*|gettimeofday*)'
Bug: 63737556
Change-Id: I81b088a12ca41a6c4733d46c5477527777138efa
diff --git a/libc/private/bionic_vdso.h b/libc/private/bionic_vdso.h
index ed11501..8c4d8d2 100644
--- a/libc/private/bionic_vdso.h
+++ b/libc/private/bionic_vdso.h
@@ -35,15 +35,18 @@
#define VDSO_CLOCK_GETTIME_SYMBOL "__kernel_clock_gettime"
#define VDSO_CLOCK_GETRES_SYMBOL "__kernel_clock_getres"
#define VDSO_GETTIMEOFDAY_SYMBOL "__kernel_gettimeofday"
+#define VDSO_TIME_SYMBOL "__kernel_time"
#else
#define VDSO_CLOCK_GETTIME_SYMBOL "__vdso_clock_gettime"
#define VDSO_CLOCK_GETRES_SYMBOL "__vdso_clock_getres"
#define VDSO_GETTIMEOFDAY_SYMBOL "__vdso_gettimeofday"
+#define VDSO_TIME_SYMBOL "__vdso_time"
#endif
extern "C" int __clock_gettime(int, timespec*);
extern "C" int __clock_getres(int, timespec*);
extern "C" int __gettimeofday(timeval*, struct timezone*);
+extern "C" time_t __time(time_t*);
struct vdso_entry {
const char* name;
@@ -54,6 +57,7 @@
VDSO_CLOCK_GETTIME = 0,
VDSO_CLOCK_GETRES,
VDSO_GETTIMEOFDAY,
+ VDSO_TIME,
VDSO_END
};