On Monday 12 February 2007 16:54, malc wrote: > On Mon, 12 Feb 2007, Con Kolivas wrote: > > On 12/02/07, Vassili Karpov <[EMAIL PROTECTED]> wrote: > > [..snip..] > > > The kernel looks at what is using cpu _only_ during the timer > > interrupt. Which means if your HZ is 1000 it looks at what is running > > at precisely the moment those 1000 timer ticks occur. It is > > theoretically possible using this measurement system to use >99% cpu > > and record 0 usage if you time your cpu usage properly. It gets even > > more inaccurate at lower HZ values for the same reason. > > Thank you very much. This somewhat contradicts what i saw (and outlined > in usnet article), namely the mplayer+/dev/rtc case. Unless ofcourse > /dev/rtc interrupt is considered to be the same as the interrupt from > PIT (on X86 that is) > > P.S. Perhaps it worth documenting this in the documentation? I caused > me, and perhaps quite a few other people, a great deal of pain and > frustration.
Lots of confusion comes from this, and often people think their pc suddenly uses a lot less cpu when they change from 1000HZ to 100HZ and use this as an argument/reason for changing to 100HZ when in fact the massive _reported_ difference is simply worse accounting. Of course there is more overhead going from 100 to 1000 but it doesn't suddenly make your apps use 10 times more cpu. -- -ck - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
