Messages in this thread | | | Subject | Re: [RFC PATCH] x86:Use cpu_khz for loops_per_jiffy calculation | From | Alok Kataria <> | Date | Thu, 26 Jun 2008 11:10:49 -0700 |
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On Thu, 2008-06-26 at 10:35 -0700, Pavel Machek wrote: > On Thu 2008-06-26 10:20:31, Alok Kataria wrote: > > On Tue, 2008-06-24 at 10:57 -0700, Pavel Machek wrote: > > > Hi! > > > > > > > On X86 platform we can use the value of tsc_khz computed during tsc calibration > > > > to calculate the loops_per_jiffy value. Its very important to keep the error in > > > > lpj values to minimum as any error in that may result in kernel panic in > > > > check_timer. > > > > In virtualization environment, On a highly overloaded host the guest delay > > > > calibration may sometimes result in errors beyond the ~50% that timer_irq_works > > > > can handle, resulting in the guest panicking. > > > > > > How did you adress 'khz has nothing to do with loops per jiffie' > > > comment? > > > > > > Some cpus can do loop in cycle , some need two cycles, some need half. > > > > Hi Pavel, > > > > When you say loops per jiffies has nothing to do with khz, by khz you > > mean the cpu frequency, right ? > > Yes. > > > AFAIU in calibrate_delay_direct too we measure the amount by which timer > > has ticked until DELAY_CALIBRATION_TICKS amount of jiffies has passed. > > So IMO the code there too assumes that there is one loop per timer > > cycle ? > > On my machine, it reports: > > delay using timer specific routine.. 3661.98 BogoMIPS (lpj=7323971) > ... > Detected 1828.828 MHz processor. > > (/proc/cpuinfo) > model name : Genuine Intel(R) CPU T2400 @ 1.83GHz > ... > cpu MHz : 1000.000 How is it 1000 here ? shouldn't this be 1830.xx > ... > bogomips : 3657.54 > > So you'd break it by setting lpj (aka bogomips) to cpu_khz, right?
We are not setting it to cpu_khz but to tsc_khz, i am assuming that in this case tsc_khz will be different than cpu_khz. Can you please mail me the full dmesg log.
Thanks, Alok > > Pavel > -- > (english) http://www.livejournal.com/~pavelmachek > (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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