Messages in this thread | | | Date | Tue, 23 Sep 2008 22:03:45 +0200 (CEST) | From | Thomas Gleixner <> | Subject | Re: Unified tracing buffer |
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On Tue, 23 Sep 2008, Martin Bligh wrote:
> >> > Yup, explains your TSC observation. Nothing we can do about. Broken by > >> > system design :( Welcome in the wonderful world of Inhell/BIOS/ACPI ! > >> > >> We have linux patches that sync the TSC on exit_idle. I'll see if I can get > >> Michael to send them out. > > > > Are you sure that they sync it precicely enough that there is no user > > space observable way of time going backwards between cores ? > > I think the tolerance is about 500 cycles. If that's not sufficient, I guess > we'll have to either live with some slight misordering (which people have > pointed out is kind of inevitable anyway) on these broken machines? > It was sufficient for what we were using it for, but maybe not for everyone.
Well, I dont care about the trace reordering at all. I care about user space visible time going backwards issues observed via the gettimeofday vsyscall. 500 cycles should be fine, I doubt that we can migrate in less than that :)
I guess you try this only for machines where the TSC runs with constant frequency, right ?
Looking forward to your patches.
Thanks,
tglx
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