Messages in this thread | | | Date | Mon, 10 Oct 2005 14:42:43 +0200 (CEST) | From | Roman Zippel <> | Subject | Re: [PATCH] ktimers subsystem 2.6.14-rc2-kt5 |
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Hi,
On Sat, 1 Oct 2005, Ingo Molnar wrote:
> > Do you have any numbers (besides maybe microbenchmarks) that show a > > real advantage by using per cpu data? What kind of usage do you expect > > here? > > it has countless advantages, and these days we basically only design > per-CPU data structures within the kernel, unless some limitation (such > as API or hw property) forces us to do otherwise. So i turn around the > question: what would be your reason for _not_ doing this clean per-CPU > design for SMP systems?
Did I say I'm against it? No, I was just hoping someone put some more thought into it than just "all the other kids are doing it". I was just curious how well it really scales compared to the simple version, e.g. what happens if most timer end up on a single cpu or what happens if we want to start the timer on a different cpu. Is this so wrong that you have to go into attack mode? :(
> > The other thing is that this assumes, that all time sources are > > programmable per cpu, otherwise it will be more complicated for a time > > source to run the timers for every cpu, I don't know how safe that > > assumption is. Changing the array of structures into an array of > > pointers to the structures would allow to switch between percpu bases > > and a single base. > > yeah, and that's an assumption that simplifies things on SMP > significantly. PIT on SMP systems for HRT is so gross that it's not > funny. If anyone wants to revive that notion, please do a separate patch > and make the case convincing enough ...
Why do use "PIT on SMP" as an extreme example to reject the general concept completely? This doesn't explain, why first such a (simple) SMP design shouldn't exist and why secondly my suggestion is such a big problem.
bye, Roman - 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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