From b65d3e5f0f452e86f81d21d59b065feeb31357be Mon Sep 17 00:00:00 2001 From: Nathan Lynch Date: Thu, 4 Jun 2015 21:10:43 +0000 Subject: ARM: VDSO support Beginning with the upcoming 4.1 release, Linux on a subset of 32-bit ARM hardware will provide fast user-space implementations of the following system calls: - gettimeofday - clock_gettime The kernel implementation depends on the ARMv7 Generic Timers Extension to accelerate these system calls. So CPUs such as Cortex-A15 and -A7 benefit, while Cortex-A9, -A8, and pre-v7 CPUs do not. On systems where the VDSO does not provide any speedup, the kernel prevents the relevant symbol lookups from succeeding. On OMAP5 (Cortex-A15) gettimeofday latency decreases from ~350ns to ~120ns. On BeagleBone Black (Cortex-A8) it goes from ~650ns to ~660ns, which to my mind is an acceptable cost. Verified that no new test failures are introduced on kernels with and without the VDSO. * sysdeps/unix/sysv/linux/arm/Makefile: (sysdep_routines): Include dl-vdso. * sysdeps/unix/sysv/linux/arm/init-first.c: New file: Use VDSO routines for gettimeofday, clock_gettime if available. * sysdeps/unix/sysv/linux/arm/libc-vdso.h: New file: Declare VDSO symbols. * sysdeps/unix/sysv/linux/arm/sysdep.h: [HAVE_GETTIMEOFDAY_VSYSCALL]: Define. [HAVE_CLOCK_GETTIME_VSYSCALL]: Define. * sysdeps/unix/sysv/linux/arm/Versions: Add __vdso_clock_gettime. --- ChangeLog | 15 +++++++++++++++ 1 file changed, 15 insertions(+) (limited to 'ChangeLog') diff --git a/ChangeLog b/ChangeLog index 89c4bcfb14..0d807909c6 100644 --- a/ChangeLog +++ b/ChangeLog @@ -1,3 +1,18 @@ +2015-06-04 Nathan Lynch + + * sysdeps/unix/sysv/linux/arm/Makefile: (sysdep_routines): + Include dl-vdso. + * sysdeps/unix/sysv/linux/arm/init-first.c: New file: + Use VDSO routines for gettimeofday, clock_gettime if + available. + * sysdeps/unix/sysv/linux/arm/libc-vdso.h: New file: + Declare VDSO symbols. + * sysdeps/unix/sysv/linux/arm/sysdep.h: + [HAVE_GETTIMEOFDAY_VSYSCALL]: Define. + [HAVE_CLOCK_GETTIME_VSYSCALL]: Define. + * sysdeps/unix/sysv/linux/arm/Versions: Add + __vdso_clock_gettime. + 2015-06-04 Adhemerval Zanella * sysdeps/unix/sysv/linux/not-cancel.h (open_not_cancel): Rewrite to -- cgit 1.4.1