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    FromAndi Kleen <>
    SubjectRe: 2.6.23-rc3-mm1 - vdso and gettimeofday issues with glibc
    DateSat, 8 Sep 2007 10:57:50 +0200
    > In the vdso code:
    > 
    > static inline long vgetns(void)
    > {
    >         cycles_t (*vread)(void);
    >         vread = gtod->clock.vread;
    >         return ((vread() - gtod->clock.cycle_last) * gtod->clock.mult) >>
    >                 gtod->clock.shift;
    > }
    > 
    > 
    > Looks like an open-coded version of this in the kernel timekeeping code:
    
    vdso code needs to be all inlined because the vdso runs in ring 3 and cannot
    access other kernel code.
    
    It was opencoded it to have more control over the code (vdso requirements
    are a bit peculiar).
    
    > But the vdso version isn't doing any masking. And the mask is different for
    > different clocksources, so it has to track the underlying kernel's clocksource
    > when it gets changed.
    
    vdso effectively only supports TSC and HPET (the other clock sources are not accessible
    from ring 3)
    
    TSC doesn't need a mask, but many HPETs need a 32bit mask; good point.
    
    Does adding the mask to vgetns make the clock problems go away?
    
    -Andi
    
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