Messages in this thread |  | | Date | Sat, 13 Oct 2001 21:38:20 +0200 | From | Jamie Lokier <> | Subject | Re: Finegrained a/c/mtime was Re: Directory notification problem |
| |
Andi Kleen wrote: > > Andi Kleen says we can ignore the risk; I disagree, as there are some > > applications that cannot be trusted if the risk is plausible, and it can > > be fixed easily. > > You're misquoting me badly. I said we can ignore the risk that two > nanosecond resolution timestamps that get changed by two different cpus > with out-of-sync cycle counter on a smp system and which are fast enough > to free/aquire the inode lock in a smaller time than they're out of sync > (= giving two file changes with the same ns timestamp) can be ignored. > I implied on the systems that don't have a cycle counter and which use > jiffie resolution gettimeofday it can be also ignored, because they're > unlikely to be SMP and dying out too anyways.
Andi, sorry I misrepresented your statement.
I misread your original as saying that the risks due to SMP nanosecond scale synchronisation problems can be ignored. Implied from that, that the small risk of one SMP process modifying a file while another checks the timestamp can be ignored. I misread this way because others have suggested higher resolution solves the problem, and I believe it does not.
As you say above, multiple modifications within a single tick are not a problem, do not have to be tracked, and therefore do not require SMP sychronisation.
The SMP risk of missing a change after checking the timestamp is among the risks I consider critical for an application which must not miss the fact that a file has changed. I do not want us to repeat the mistake of 1 second at a smaller timescale.
cheers, -- Jamie - 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/
|  |