Messages in this thread | | | From | Denis Vlasenko <> | Subject | Re: [PATCH *] use 64 bit jiffies | Date | Tue, 4 Feb 2003 08:41:13 +0200 |
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On 3 February 2003 10:28, Matti Aarnio wrote: > On Mon, Feb 03, 2003 at 08:42:59AM +0200, Denis Vlasenko wrote: > > On 3 February 2003 00:55, Tim Schmielau wrote: > > > Just a note that I have rediffed for 2.5.55 the patches that use > > > the 64 bit jiffies value to avoid uptime and process start time > > > wrap after 49.5 days. I will push them Linus-wards when he's > > > back. They can be retrieved from > > .... > > > Wow... your patches are STILL not included?? > > My 2.4 based server approaches 250 days uptime, it would be a shame > > to be unable to have uptime < 50 days with 2.5 > > 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? -- vda - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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