Messages in this thread | | | Date | Wed, 22 Jul 2015 16:43:30 -0400 (EDT) | From | Mikulas Patocka <> | Subject | Re: Kernel broken on processors without performance counters |
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On Wed, 22 Jul 2015, Borislav Petkov wrote:
> On Tue, Jul 21, 2015 at 02:50:25PM -0400, Jason Baron wrote: > > hmmm...so this is a case where need to the default the branch > > to the out-of-line branch at boot. That is, we can't just enable > > the out-of-line branch at boot time, b/c it might be too late at > > that point? IE native_sched_clock() gets called very early? > > Well, even the layout is wrong here. The optimal thing would be to have: > > NOP > rdtsc > > unlikely: > /* read jiffies */ > > at build time. And then at boot time, patch in the JMP over the NOP on > !use_tsc boxes. And RDTSC works always, no matter how early.
RDTSC doesn't work on 486...
Mikulas
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