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authorAlex Smith <alex.smith@imgtec.com>2015-10-21 09:57:44 +0100
committerRalf Baechle <ralf@linux-mips.org>2015-11-11 08:36:41 +0100
commita7f4df4e21dd8a8dab96e88acd2c9c5017b83fc6 (patch)
tree36c00d0b92be2e2a39da15839f4bfe09be72b572 /arch/mips/Kconfig
parentc0a9f72c156baf1e88c33c6ba4450647af1b8804 (diff)
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/Kconfig')
-rw-r--r--arch/mips/Kconfig5
1 files changed, 5 insertions, 0 deletions
diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig
index 9322d267e774..2f45c866e7ca 100644
--- a/arch/mips/Kconfig
+++ b/arch/mips/Kconfig
@@ -61,6 +61,8 @@ config MIPS
select SYSCTL_EXCEPTION_TRACE
select HAVE_VIRT_CPU_ACCOUNTING_GEN
select HAVE_IRQ_TIME_ACCOUNTING
+ select GENERIC_TIME_VSYSCALL
+ select ARCH_CLOCKSOURCE_DATA
menu "Machine selection"
@@ -1040,6 +1042,9 @@ config CSRC_R4K
config CSRC_SB1250
bool
+config MIPS_CLOCK_VSYSCALL
+ def_bool CSRC_R4K || CLKSRC_MIPS_GIC
+
config GPIO_TXX9
select ARCH_REQUIRE_GPIOLIB
bool