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SubjectRe: [patch][rfc] enable uptime display > 497 days on 32 bit
On Feb 26, 2002  11:42 -0800, george anzinger wrote:
> Well, since you asked (thank you), the high-res-timers patch needs to
> get the full 64-bit uptime to implement CLOCK_MONOTONIC.
> This means that the 64-bit jiffies is used "often" in this code.
> Unlike this patch, it keeps the 64-bit rational (i.e. always current)

Well, if you use the get_jiffies64() interface the 64-bit value is
always coherent as well, and the direct access to the 32-bit value
is monotonic. While the high and low words of the 64-bit jiffies
values may be incoherent at times, as long as you always access the
64-bit value with the get_jiffies64() interface it should be OK.

Do you think that doing a 64-bit add-with-carry to memory on each
timer interrupt and doing multiple volatile reads is faster than
doing a spinlock with an optional 32-bit increment? Do you think
there would be a lot of contention on this lock, given that you
only need to lock when you need the full 64-bit value?

Cheers, Andreas
Andreas Dilger

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