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On Fri, Oct 05, 2001 at 01:44:20PM +0100, Padraig Brady wrote: > Andi Kleen wrote: > > >On Wed, Oct 03, 2001 at 11:15:04AM -0400, Alex Larsson wrote: > > > >>Is a nanoseconds field the right choice though? In reality you might not > >>have a nanosecond resolution timer, so you would miss changes that appear > >>on shorter timescale than the timer resolution. Wouldn't a generation > >>counter, increased when ctime was updated, be a better solution? > >> > > > >Near any CPU has a cycle counter builtin now, which gives you ns like > >resolution. In theory you could still get collisions on MP systems, > >but window is small enough that it can be ignored in practice. > > > >-Andi > > > But the point is you, only ever would want nano second resolution to make > sure you notice all changes to a file. A more general (and much simpler) > solution would be to gen_count++ every time a file's modified. What other > applications would require better than second resolution on files? The main advantage of using a real timestamp instead of a generation counter is that we would be compatible to Unixware/Solaris/... Their API is fine, so I see no advantage in inventing a new incompatible one. Another advantage of using the real time instead of a counter is that you can easily merge the both values into a single 64bit value and do arithmetic on it in user space. With a generation counter you would need to work with number pairs, which is much more complex. [or alternatively reset the generation counter every second in the kernel to get a flat time range again, which would be racy and ugly and complicated in the kernel because it would need additional timestamps] Also a rdtsc/get_timestamp or in the worst case a jiffie read is really not complex to code in kernel, what makes you think it is? -Andi - 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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