Re: [patch][rfc] enable uptime display > 497 days on 32 bit

[Andreas Dilger]

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
http://sourceforge.net/projects/ext2resize/
http://www-mddsp.enel.ucalgary.ca/People/adilger/