To allow constant folding in usecs_to_jiffies() conditionally calls the HZ dependent _usecs_to_jiffies() helpers or, when gcc can not figure out constant folding, __usecs_to_jiffies, which is the renamed original usecs_to_jiffies() function.
Patch was build tested for: arm - imx_v6_v7_defconfig, vexpress_defconfig cris - etrax-100lx_v2_defconfig ia64 - generic_defconfig (though with lots of build warnings both with and without patch) m68k - multi_defconfig mips32 - ar7_defconfig, mips64 - loongson3_defconfig powerpc - 44x/virtex5_defconfig powerpc64 - ppc64_defconfig s390 - failed to build for all defconfigs with toolchain from kernel.org (cc1: error: unrecognized command line option '-mtune=zEC12') sh - se7780_defconfig, sparc32 - sparc32_defconfig sparc64 - sparc64_defconfig x86 64 - x86_64_defconfig, patch is against 4.1-rc5 (localversion-next is -next-20150527) Link: http://lkml.org/lkml/2015/5/18/274 Signed-off-by: Nicholas Mc Guire <hof...@osadl.org> --- Thanks to Joe Perches <j...@perches.com> for suggesting this approach. and helping with the initial msecs_to_jiffies cleanup patch. Verification of const folding: config: x86_64_defconfig + CONFIG_DRM_GMA500=m, CONFIG_DRM_GMA3600=y drivers/gpu/drm/gma500/intel_gmbus.c 204 gpio->algo.timeout = usecs_to_jiffies(2200); -> reduced to load instruction config: x86_64_defconfig + CONFIG_INFINIBAND=m, CONFIG_INFINIBAND_QIB=m drivers/infiniband/hw/qib/qib_qp.c 809 qp->timeout = attr->timeout; 810 qp->timeout_jiffies = 811 usecs_to_jiffies((4096UL * (1UL << qp->timeout)) / 812 1000UL); -> call __usecs_to_jiffies include/linux/jiffies.h | 30 +++++++++++++++++++++++++++++- 1 file changed, 29 insertions(+), 1 deletion(-) diff --git a/include/linux/jiffies.h b/include/linux/jiffies.h index cf6eaaf..c0aa150 100644 --- a/include/linux/jiffies.h +++ b/include/linux/jiffies.h @@ -383,9 +383,37 @@ static inline unsigned long _usecs_to_jiffies(const unsigned int u) } #endif +/** + * usecs_to_jiffies: - convert microseconds to jiffies + * @u: time in microseconds + * + * conversion is done as follows: + * + * - 'too large' values [that would result in larger than + * MAX_JIFFY_OFFSET values] mean 'infinite timeout' too. + * + * - all other values are converted to jiffies by either multiplying + * the input value by a factor or dividing it with a factor and + * handling any 32-bit overflows as for msecs_to_jiffies. + * + * usecs_to_jiffies() checks for the passed in value being a constant + * via __builtin_constant_p() allowing gcc to eliminate most of the + * code, __usecs_to_jiffies() is called if the value passed does not + * allow constant folding and the actual conversion must be done at + * runtime. + * the HZ range specific helpers _usecs_to_jiffies() are called both + * directly here and from __msecs_to_jiffies() in the case where + * constant folding is not possible. + */ static inline unsigned long usecs_to_jiffies(const unsigned int u) { - return __usecs_to_jiffies(u); + if (__builtin_constant_p(u)) { + if (u > jiffies_to_usecs(MAX_JIFFY_OFFSET)) + return MAX_JIFFY_OFFSET; + return _usecs_to_jiffies(u); + } else { + return __usecs_to_jiffies(u); + } } extern unsigned long timespec_to_jiffies(const struct timespec *value); -- 1.7.10.4 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
