From mboxrd@z Thu Jan 1 00:00:00 1970 From: arnd@arndb.de (Arnd Bergmann) Date: Wed, 03 Dec 2014 21:03:48 +0100 Subject: [PATCH] optimize ktime_divns for constant divisors In-Reply-To: References: Message-ID: <3913269.qTFsa05Ysv@wuerfel> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Wednesday 03 December 2014 14:43:06 Nicolas Pitre wrote: > At least on ARM, do_div() is optimized to turn constant divisors into > an inline multiplication by the reciprocal value at compile time. > However this optimization is missed entirely whenever ktime_divns() is > used and the slow out-of-line division code is used all the time. > > Let ktime_divns() use do_div() inline whenever the divisor is constant > and small enough. This will make things like ktime_to_us() and > ktime_to_ms() much faster. > > Signed-off-by: Nicolas Pitre Very cool. I've been thinking about doing something similar for the general case but couldn't get the math to work. Can you think of an architecture-independent way to ktime_to_sec, ktime_to_ms, and ktime_to_us efficiently based on what you did for the ARM do_div implementation? Arnd