Re: [PATCH *] use 64 bit jiffies

Randy.Dunlap
2003-02-04T17:30:40Z

On Tue, 4 Feb 2003, Denis Vlasenko wrote:

| On 3 February 2003 10:28, Matti Aarnio wrote:
| >
| > You don't need to have 64-bit jiffy for things like internal
| > timers, nor for uptime tracking.
| >
| > Timers have well behaving constructs to use 32-bit jiffy quite
| > successfully, and 64-bit values, especially atomicish, in 32-bit
| > register-poor machines (i386) are damn difficult.
| >
| > I do have a number of machines with 100 to 300 day uptimes, all
| > with "mere" 32-bit jiffy. With 1000 Hz clock that means at least
| > one full wrap-around of jiffy.
|
| Your processes will show strange start times, CPU times etc.
| This will happen in 2.5 pretty soon (after 50 days uptime).
|
| However, this is a bit cosmetic. There is a much more serious problem:
|
| Jiffy Wrap Bugs
|
| There were reports of machines hanging on jiffy wrap.
| This is typically a result of incorrect jiffy use in some driver.
| Ask Tim - he is hunting those problems regularly, but he is outnumbered
| by buggy driver authors. :(
|
| There is a better solution to ensure correct jiffy wrap handling in
| *ALL* kernel code: make jiffy wrap in first five minutes of uptime.
| Tim has a patch for such config option. This is almost right.
| This MUST NOT be a config option, it MUST be mandatory in every
| kernel. Driver writers would be bitten by their own bugs and will
| fix it themself. Tim, what do you think?

I like it too. We should take advantage of easy-to-force/find/fix
problems like this.

--
~Randy