vDSO (virtual dynamic shared object) is a mechanism that the Linux kernel provides as an alternative to system calls to reduce where possible the costs in terms of cycles. This is possible because certain syscalls like gettimeofday() do not write any data and return one or more values that are stored in the kernel, which makes relatively safe calling them directly as a library function.
Even if the mechanism is pretty much standard, every architecture in the last few years ended up implementing their own vDSO library in the architectural code.
The purpose of this patch-set is to identify the commonalities in between the architectures and try to consolidate the common code paths, starting with gettimeofday().
This implementation contains the following design choices: * Every architecture defines the arch specific code in an header in "asm/vdso/". * The generic implementation includes the arch specific one and lives in "lib/vdso". * The arch specific code for gettimeofday lives in "<arch path>/vdso/gettimeofday.c" and includes the generic code only. * The generic implementation of update_vsyscall and update_vsyscall_tz lives in kernel/vdso and provide the bindings that can be implemented by each architecture. * Each architecture provides its implementation of the bindings in "asm/vdso/vsyscall.h". * This approach allows to consolidate the common code in a single place with the benefit of avoiding code duplication.
This implementation contains the portings to the common library for: arm64, compat mode for arm64, arm, mips, x86_64, x32, compat mode for x86_64 and i386.
The mips porting has been tested on qemu for mips32el. A configuration to repeat the tests can be found at [4].
The x86_64 porting has been tested on an Intel Xeon 5120T based machine running Ubuntu 18.04 and using the Ubuntu provided defconfig.
The i386 porting has been tested on qemu using the i386_defconfig configuration.
Last but not least from this porting arm64, compat arm64, arm and mips gain the support for: * CLOCK_BOOTTIME that can be useful in certain scenarios since it keeps track of the time during sleep as well. * CLOCK_TAI that is like CLOCK_REALTIME, but uses the International Atomic Time (TAI) reference instead of UTC to avoid jumping on leap second updates. for both clock_gettime and clock_getres.
The porting has been validated using the vdsotest test-suite [1] extended to cover all the clock ids [2].
A new test has been added to the linux kselftest in order to validate the newly added library.
The porting has been benchmarked and the performance results are provided as part of this cover letter.
To simplify the testing, a copy of the patchset on top of a recent linux tree can be found at [3] and [4].
[1] https://github.com/nathanlynch/vdsotest [2] https://github.com/fvincenzo/vdsotest [3] git://linux-arm.org/linux-vf.git vdso/v6 [4] git://linux-arm.org/linux-vf.git vdso-mips/v6
Changes: -------- v6: - Rebased on 5.2-rc2. - Added performance numbers. - Removed vdso_types.h. - Unified update_vsyscall and update_vsyscall_tz. - Reworked the kselftest included in this patchset. - Addressed review comments. v5: - Rebased on 5.0-rc7. - Added x86_64, compat mode for x86_64 and i386 portings. - Extended vDSO kselftest. - Addressed review comments. v4: - Rebased on 5.0-rc2. - Addressed review comments. - Disabled compat vdso on arm64 when the kernel is compiled with clang. v3: - Ported the latest fixes and optimizations done on the x86 architecture to the generic library. - Addressed review comments. - Improved the documentation of the interfaces. - Changed the HAVE_ARCH_TIMER config option to a more generic HAVE_HW_COUNTER. v2: - Added -ffixed-x18 to arm64 - Repleced occurrences of timeval and timespec - Modified datapage.h to be compliant with y2038 on all the architectures - Removed __u_vdso type
Cc: Catalin Marinas catalin.marinas@arm.com Cc: Will Deacon will.deacon@arm.com Cc: Arnd Bergmann arnd@arndb.de Cc: Russell King linux@armlinux.org.uk Cc: Ralf Baechle ralf@linux-mips.org Cc: Paul Burton paul.burton@mips.com Cc: Daniel Lezcano daniel.lezcano@linaro.org Cc: Thomas Gleixner tglx@linutronix.de Cc: Mark Salyzyn salyzyn@android.com Cc: Peter Collingbourne pcc@google.com Cc: Shuah Khan shuah@kernel.org Cc: Dmitry Safonov 0x7f454c46@gmail.com Cc: Rasmus Villemoes linux@rasmusvillemoes.dk Cc: Huw Davies huw@codeweavers.com Signed-off-by: Vincenzo Frascino vincenzo.frascino@arm.com
Performance Numbers: Linux 5.2.0-rc2 - Xeon Gold 5120T ======================================================
Unified vDSO: -------------
clock-gettime-monotonic: syscall: 342 nsec/call clock-gettime-monotonic: libc: 25 nsec/call clock-gettime-monotonic: vdso: 24 nsec/call clock-getres-monotonic: syscall: 296 nsec/call clock-getres-monotonic: libc: 296 nsec/call clock-getres-monotonic: vdso: 3 nsec/call clock-gettime-monotonic-coarse: syscall: 294 nsec/call clock-gettime-monotonic-coarse: libc: 5 nsec/call clock-gettime-monotonic-coarse: vdso: 5 nsec/call clock-getres-monotonic-coarse: syscall: 295 nsec/call clock-getres-monotonic-coarse: libc: 292 nsec/call clock-getres-monotonic-coarse: vdso: 5 nsec/call clock-gettime-monotonic-raw: syscall: 343 nsec/call clock-gettime-monotonic-raw: libc: 25 nsec/call clock-gettime-monotonic-raw: vdso: 23 nsec/call clock-getres-monotonic-raw: syscall: 290 nsec/call clock-getres-monotonic-raw: libc: 290 nsec/call clock-getres-monotonic-raw: vdso: 4 nsec/call clock-gettime-tai: syscall: 332 nsec/call clock-gettime-tai: libc: 24 nsec/call clock-gettime-tai: vdso: 23 nsec/call clock-getres-tai: syscall: 288 nsec/call clock-getres-tai: libc: 288 nsec/call clock-getres-tai: vdso: 3 nsec/call clock-gettime-boottime: syscall: 342 nsec/call clock-gettime-boottime: libc: 24 nsec/call clock-gettime-boottime: vdso: 23 nsec/call clock-getres-boottime: syscall: 284 nsec/call clock-getres-boottime: libc: 291 nsec/call clock-getres-boottime: vdso: 3 nsec/call clock-gettime-realtime: syscall: 337 nsec/call clock-gettime-realtime: libc: 24 nsec/call clock-gettime-realtime: vdso: 23 nsec/call clock-getres-realtime: syscall: 287 nsec/call clock-getres-realtime: libc: 284 nsec/call clock-getres-realtime: vdso: 3 nsec/call clock-gettime-realtime-coarse: syscall: 307 nsec/call clock-gettime-realtime-coarse: libc: 4 nsec/call clock-gettime-realtime-coarse: vdso: 4 nsec/call clock-getres-realtime-coarse: syscall: 294 nsec/call clock-getres-realtime-coarse: libc: 291 nsec/call clock-getres-realtime-coarse: vdso: 4 nsec/call getcpu: syscall: 246 nsec/call getcpu: libc: 14 nsec/call getcpu: vdso: 11 nsec/call gettimeofday: syscall: 293 nsec/call gettimeofday: libc: 26 nsec/call gettimeofday: vdso: 25 nsec/call
Stock Kernel: -------------
clock-gettime-monotonic: syscall: 338 nsec/call clock-gettime-monotonic: libc: 24 nsec/call clock-gettime-monotonic: vdso: 23 nsec/call clock-getres-monotonic: syscall: 291 nsec/call clock-getres-monotonic: libc: 304 nsec/call clock-getres-monotonic: vdso: not tested Note: vDSO version of clock_getres not found clock-gettime-monotonic-coarse: syscall: 297 nsec/call clock-gettime-monotonic-coarse: libc: 5 nsec/call clock-gettime-monotonic-coarse: vdso: 4 nsec/call clock-getres-monotonic-coarse: syscall: 281 nsec/call clock-getres-monotonic-coarse: libc: 286 nsec/call clock-getres-monotonic-coarse: vdso: not tested Note: vDSO version of clock_getres not found clock-gettime-monotonic-raw: syscall: 336 nsec/call clock-gettime-monotonic-raw: libc: 340 nsec/call clock-gettime-monotonic-raw: vdso: 346 nsec/call clock-getres-monotonic-raw: syscall: 297 nsec/call clock-getres-monotonic-raw: libc: 301 nsec/call clock-getres-monotonic-raw: vdso: not tested Note: vDSO version of clock_getres not found clock-gettime-tai: syscall: 351 nsec/call clock-gettime-tai: libc: 24 nsec/call clock-gettime-tai: vdso: 23 nsec/call clock-getres-tai: syscall: 298 nsec/call clock-getres-tai: libc: 290 nsec/call clock-getres-tai: vdso: not tested Note: vDSO version of clock_getres not found clock-gettime-boottime: syscall: 342 nsec/call clock-gettime-boottime: libc: 347 nsec/call clock-gettime-boottime: vdso: 355 nsec/call clock-getres-boottime: syscall: 296 nsec/call clock-getres-boottime: libc: 295 nsec/call clock-getres-boottime: vdso: not tested Note: vDSO version of clock_getres not found clock-gettime-realtime: syscall: 346 nsec/call clock-gettime-realtime: libc: 24 nsec/call clock-gettime-realtime: vdso: 22 nsec/call clock-getres-realtime: syscall: 295 nsec/call clock-getres-realtime: libc: 291 nsec/call clock-getres-realtime: vdso: not tested Note: vDSO version of clock_getres not found clock-gettime-realtime-coarse: syscall: 292 nsec/call clock-gettime-realtime-coarse: libc: 5 nsec/call clock-gettime-realtime-coarse: vdso: 4 nsec/call clock-getres-realtime-coarse: syscall: 300 nsec/call clock-getres-realtime-coarse: libc: 301 nsec/call clock-getres-realtime-coarse: vdso: not tested Note: vDSO version of clock_getres not found getcpu: syscall: 252 nsec/call getcpu: libc: 14 nsec/call getcpu: vdso: 11 nsec/call gettimeofday: syscall: 293 nsec/call gettimeofday: libc: 24 nsec/call gettimeofday: vdso: 25 nsec/call
Peter Collingbourne (1): arm64: Build vDSO with -ffixed-x18
Vincenzo Frascino (18): kernel: Standardize vdso_datapage kernel: Define gettimeofday vdso common code kernel: Unify update_vsyscall implementation arm64: Substitute gettimeofday with C implementation arm64: compat: Add missing syscall numbers arm64: compat: Expose signal related structures arm64: compat: Generate asm offsets for signals lib: vdso: Add compat support arm64: compat: Add vDSO arm64: Refactor vDSO code arm64: compat: vDSO setup for compat layer arm64: elf: vDSO code page discovery arm64: compat: Get sigreturn trampolines from vDSO arm64: Add vDSO compat support arm: Add support for generic vDSO mips: Add support for generic vDSO x86: Add support for generic vDSO kselftest: Extend vDSO selftest
arch/arm/Kconfig | 3 + arch/arm/include/asm/vdso/gettimeofday.h | 96 +++++ arch/arm/include/asm/vdso/vsyscall.h | 71 ++++ arch/arm/include/asm/vdso_datapage.h | 29 +- arch/arm/kernel/vdso.c | 87 +---- arch/arm/vdso/Makefile | 13 +- arch/arm/vdso/note.c | 15 + arch/arm/vdso/vdso.lds.S | 2 + arch/arm/vdso/vgettimeofday.c | 268 +------------ arch/arm64/Kconfig | 3 + arch/arm64/Makefile | 23 +- arch/arm64/include/asm/elf.h | 14 + arch/arm64/include/asm/signal32.h | 46 +++ arch/arm64/include/asm/unistd.h | 5 + arch/arm64/include/asm/vdso.h | 3 + arch/arm64/include/asm/vdso/compat_barrier.h | 51 +++ .../include/asm/vdso/compat_gettimeofday.h | 108 ++++++ arch/arm64/include/asm/vdso/gettimeofday.h | 84 +++++ arch/arm64/include/asm/vdso/vsyscall.h | 53 +++ arch/arm64/include/asm/vdso_datapage.h | 48 --- arch/arm64/kernel/Makefile | 6 +- arch/arm64/kernel/asm-offsets.c | 39 +- arch/arm64/kernel/signal32.c | 72 ++-- arch/arm64/kernel/vdso.c | 356 ++++++++++++------ arch/arm64/kernel/vdso/Makefile | 34 +- arch/arm64/kernel/vdso/gettimeofday.S | 334 ---------------- arch/arm64/kernel/vdso/vgettimeofday.c | 28 ++ arch/arm64/kernel/vdso32/.gitignore | 2 + arch/arm64/kernel/vdso32/Makefile | 184 +++++++++ arch/arm64/kernel/vdso32/note.c | 15 + arch/arm64/kernel/vdso32/sigreturn.S | 62 +++ arch/arm64/kernel/vdso32/vdso.S | 19 + arch/arm64/kernel/vdso32/vdso.lds.S | 82 ++++ arch/arm64/kernel/vdso32/vgettimeofday.c | 59 +++ arch/mips/Kconfig | 2 + arch/mips/include/asm/vdso.h | 78 +--- arch/mips/include/asm/vdso/gettimeofday.h | 175 +++++++++ arch/mips/{ => include/asm}/vdso/vdso.h | 6 +- arch/mips/include/asm/vdso/vsyscall.h | 43 +++ arch/mips/kernel/vdso.c | 37 +- arch/mips/vdso/Makefile | 25 +- arch/mips/vdso/elf.S | 2 +- arch/mips/vdso/gettimeofday.c | 273 -------------- arch/mips/vdso/sigreturn.S | 2 +- arch/mips/vdso/vdso.lds.S | 4 + arch/mips/vdso/vgettimeofday.c | 57 +++ arch/x86/Kconfig | 3 + arch/x86/entry/vdso/Makefile | 9 + arch/x86/entry/vdso/vclock_gettime.c | 251 +++--------- arch/x86/entry/vdso/vdso.lds.S | 2 + arch/x86/entry/vdso/vdso32/vdso32.lds.S | 2 + arch/x86/entry/vdso/vdsox32.lds.S | 1 + arch/x86/entry/vsyscall/Makefile | 2 - arch/x86/entry/vsyscall/vsyscall_gtod.c | 83 ---- arch/x86/include/asm/mshyperv-tsc.h | 76 ++++ arch/x86/include/asm/mshyperv.h | 70 +--- arch/x86/include/asm/pvclock.h | 2 +- arch/x86/include/asm/vdso/gettimeofday.h | 203 ++++++++++ arch/x86/include/asm/vdso/vsyscall.h | 44 +++ arch/x86/include/asm/vgtod.h | 75 +--- arch/x86/include/asm/vvar.h | 7 +- arch/x86/kernel/pvclock.c | 1 + include/asm-generic/vdso/vsyscall.h | 56 +++ include/linux/hrtimer.h | 15 +- include/linux/hrtimer_defs.h | 25 ++ include/linux/timekeeper_internal.h | 9 + include/vdso/datapage.h | 91 +++++ include/vdso/helpers.h | 56 +++ include/vdso/vsyscall.h | 11 + kernel/Makefile | 1 + kernel/vdso/Makefile | 2 + kernel/vdso/vsyscall.c | 139 +++++++ lib/Kconfig | 5 + lib/vdso/Kconfig | 36 ++ lib/vdso/Makefile | 22 ++ lib/vdso/gettimeofday.c | 229 +++++++++++ tools/testing/selftests/vDSO/Makefile | 2 + tools/testing/selftests/vDSO/vdso_full_test.c | 261 +++++++++++++ 78 files changed, 3042 insertions(+), 1767 deletions(-) create mode 100644 arch/arm/include/asm/vdso/gettimeofday.h create mode 100644 arch/arm/include/asm/vdso/vsyscall.h create mode 100644 arch/arm/vdso/note.c create mode 100644 arch/arm64/include/asm/vdso/compat_barrier.h create mode 100644 arch/arm64/include/asm/vdso/compat_gettimeofday.h create mode 100644 arch/arm64/include/asm/vdso/gettimeofday.h create mode 100644 arch/arm64/include/asm/vdso/vsyscall.h delete mode 100644 arch/arm64/include/asm/vdso_datapage.h delete mode 100644 arch/arm64/kernel/vdso/gettimeofday.S create mode 100644 arch/arm64/kernel/vdso/vgettimeofday.c create mode 100644 arch/arm64/kernel/vdso32/.gitignore create mode 100644 arch/arm64/kernel/vdso32/Makefile create mode 100644 arch/arm64/kernel/vdso32/note.c create mode 100644 arch/arm64/kernel/vdso32/sigreturn.S create mode 100644 arch/arm64/kernel/vdso32/vdso.S create mode 100644 arch/arm64/kernel/vdso32/vdso.lds.S create mode 100644 arch/arm64/kernel/vdso32/vgettimeofday.c create mode 100644 arch/mips/include/asm/vdso/gettimeofday.h rename arch/mips/{ => include/asm}/vdso/vdso.h (90%) create mode 100644 arch/mips/include/asm/vdso/vsyscall.h delete mode 100644 arch/mips/vdso/gettimeofday.c create mode 100644 arch/mips/vdso/vgettimeofday.c delete mode 100644 arch/x86/entry/vsyscall/vsyscall_gtod.c create mode 100644 arch/x86/include/asm/mshyperv-tsc.h create mode 100644 arch/x86/include/asm/vdso/gettimeofday.h create mode 100644 arch/x86/include/asm/vdso/vsyscall.h create mode 100644 include/asm-generic/vdso/vsyscall.h create mode 100644 include/linux/hrtimer_defs.h create mode 100644 include/vdso/datapage.h create mode 100644 include/vdso/helpers.h create mode 100644 include/vdso/vsyscall.h create mode 100644 kernel/vdso/Makefile create mode 100644 kernel/vdso/vsyscall.c create mode 100644 lib/vdso/Kconfig create mode 100644 lib/vdso/Makefile create mode 100644 lib/vdso/gettimeofday.c create mode 100644 tools/testing/selftests/vDSO/vdso_full_test.c