On Mon, Nov 21, 2016 at 7:28 AM, Chris Metcalf <cmetc...@mellanox.com> wrote: > On 11/21/2016 3:54 AM, Ingo Molnar wrote: >> >> * John Stultz <john.stu...@linaro.org> wrote: >> >>> From: Chris Metcalf <cmetc...@mellanox.com> >>> >>> The "cycles" argument should not be an absolute clocksource cycle >>> value, as the implementation's arithmetic will overflow relatively >>> easily with wide (64 bit) clocksource counters. >>> >>> For performance, the implementation is simple and fast, since the >>> function is intended for only relatively small delta values of >>> clocksource cycles. >>> >>> Cc: Richard Cochran <richardcoch...@gmail.com> >>> Cc: Ingo Molnar <mi...@kernel.org> >>> Cc: Prarit Bhargava <pra...@redhat.com> >>> Cc: Thomas Gleixner <t...@linutronix.de> >>> Signed-off-by: Chris Metcalf <cmetc...@mellanox.com> >>> [jstultz: Fixed up to merge against HEAD & commit message tweaks] >>> Signed-off-by: John Stultz <john.stu...@linaro.org> >>> --- >>> include/linux/clocksource.h | 5 ++++- >>> 1 file changed, 4 insertions(+), 1 deletion(-) >>> >>> diff --git a/include/linux/clocksource.h b/include/linux/clocksource.h >>> index 0839818..0881bca 100644 >>> --- a/include/linux/clocksource.h >>> +++ b/include/linux/clocksource.h >>> @@ -169,7 +169,10 @@ static inline u32 clocksource_hz2mult(u32 hz, u32 >>> shift_constant) >>> * @mult: cycle to nanosecond multiplier >>> * @shift: cycle to nanosecond divisor (power of two) >>> * >>> - * Converts cycles to nanoseconds, using the given mult and shift. >>> + * Converts clocksource cycles to nanoseconds, using the given mult and >>> shift. >>> + * The code is optimized for performance and not intended to work >>> + * with absolute clocksource cycles, as it will easily overflow, >>> + * but just intended for relative (delta) clocksource cycles. >> >> Had to read this explanation twice, how about: >> >> * Converts clocksource cycles to nanoseconds, using the given @mult >> and @shift. >> * The code is optimized for performance and is not intended to work >> * with absolute clocksource cycles (as those will easily overflow), >> * but is only intended to be used with relative (delta) clocksource >> cycles. >> >> Did I get it right? > > > Yes, I think that's an improvement. Thanks! > > John, I assume you can just fix this up?
Sure. Reworded to take Ingo's suggestions. thanks -john
