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author | Alex Smith <alex.smith@imgtec.com> | 2015-10-21 11:57:44 +0300 |
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committer | Ralf Baechle <ralf@linux-mips.org> | 2015-11-11 10:36:41 +0300 |
commit | a7f4df4e21dd8a8dab96e88acd2c9c5017b83fc6 (patch) | |
tree | 36c00d0b92be2e2a39da15839f4bfe09be72b572 /arch/mips/vdso/vdso.lds.S | |
parent | c0a9f72c156baf1e88c33c6ba4450647af1b8804 (diff) | |
download | linux-a7f4df4e21dd8a8dab96e88acd2c9c5017b83fc6.tar.xz |
MIPS: VDSO: Add implementations of gettimeofday() and clock_gettime()
Add user-mode implementations of gettimeofday() and clock_gettime() to
the VDSO. This is currently usable with 2 clocksources: the CP0 count
register, which is accessible to user-mode via RDHWR on R2 and later
cores, or the MIPS Global Interrupt Controller (GIC) timer, which
provides a "user-mode visible" section containing a mirror of its
counter registers. This section must be mapped into user memory, which
is done below the VDSO data page.
When a supported clocksource is not in use, the VDSO functions will
return -ENOSYS, which causes libc to fall back on the standard syscall
path.
When support for neither of these clocksources is compiled into the
kernel at all, the VDSO still provides clock_gettime(), as the coarse
realtime/monotonic clocks can still be implemented. However,
gettimeofday() is not provided in this case as nothing can be done
without a suitable clocksource. This causes the symbol lookup to fail
in libc and it will then always use the standard syscall path.
This patch includes a workaround for a bug in QEMU which results in
RDHWR on the CP0 count register always returning a constant (incorrect)
value. A fix for this has been submitted, and the workaround can be
removed after the fix has been in stable releases for a reasonable
amount of time.
A simple performance test which calls gettimeofday() 1000 times in a
loop and calculates the average execution time gives the following
results on a Malta + I6400 (running at 20MHz):
- Syscall: ~31000 ns
- VDSO (GIC): ~15000 ns
- VDSO (CP0): ~9500 ns
[markos.chandras@imgtec.com:
- Minor code re-arrangements in order for mappings to be made
in the order they appear to the process' address space.
- Move do_{monotonic, realtime} outside of the MIPS_CLOCK_VSYSCALL ifdef
- Use gic_get_usm_range so we can do the GIC mapping in the
arch/mips/kernel/vdso instead of the GIC irqchip driver]
Signed-off-by: Alex Smith <alex.smith@imgtec.com>
Signed-off-by: Markos Chandras <markos.chandras@imgtec.com>
Cc: linux-kernel@vger.kernel.org
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/11338/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
Diffstat (limited to 'arch/mips/vdso/vdso.lds.S')
-rw-r--r-- | arch/mips/vdso/vdso.lds.S | 5 |
1 files changed, 5 insertions, 0 deletions
diff --git a/arch/mips/vdso/vdso.lds.S b/arch/mips/vdso/vdso.lds.S index 21655b6fefc5..8df7dd53e8e0 100644 --- a/arch/mips/vdso/vdso.lds.S +++ b/arch/mips/vdso/vdso.lds.S @@ -95,6 +95,11 @@ PHDRS VERSION { LINUX_2.6 { +#ifndef DISABLE_MIPS_VDSO + global: + __vdso_clock_gettime; + __vdso_gettimeofday; +#endif local: *; }; } |