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Date: Wed, 30 Nov 2011 10:43:19 -0800 From: John Stultz <johnstul@...ibm.com> To: "Yang Honggang(Joseph)" <ganggexiongqi@...il.com> Cc: linux-kernel@...r.kernel.org Subject: Re: clocksource.c "margin" On Wed, 2011-11-30 at 19:09 -0500, Yang Honggang(Joseph) wrote: > Hi John Stultz, > I'm very sorry to trouble you. A problem puzzled me when I reading your > code in kernel/time/clocksource.c. > In the following functions, your said in the comments that >>5 was used > to leave a margin of 12.5%. > I don't know how to get the result. I think is should be >> 3 in order > to leave a margin of 12.5%. > The operation of >> 5 only left 3.125% margin. > > __clocksource_updatefreq_scale > ... > sec = (cs->mask - (cs->mask >> 5)); > ... > clocksource_max_deferment > ... > /* > * To ensure that the clocksource does not wrap whilst we are idle, > * limit the time the clocksource can be deferred by 12.5%. Please > * note a margin of 12.5% is used because this can be computed with > * a shift, versus say 10% which would require division. > */ > return max_nsecs - (max_nsecs >> 5); > ... Indeed. This looks wrong. Would you like to send a patch in correcting this issue? If not, let me know and I'll do so. thanks -john -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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