Messages in this thread | | | Date | Mon, 12 Jun 2006 15:07:23 +0200 | From | Ingo Molnar <> | Subject | Re: 2.6.16-rc6-mm2 |
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* Andi Kleen <ak@suse.de> wrote:
> > below is an updated patch that includes fixups for i386 - but the real > > fix should be to properly reduce the per-arch local.h footprint to the > > bare minimum possible, and to do this fix on the asm-generic headers. > > I think an even better approach would be to use local_save_flags() / > local_restore_flags () and then use a normal increment and get rid of > smp_processor_id completely.
local_irq_save()/local_irq_restore() you must have meant :-)
> I've never seen any evidence that the complex and bloated code > generated by this is any better that just enabling/disabling > interrupts. > > In the x86 world P4 has costly cli/sti, but I wouldn't expect that > problem to be very widespread.
i think you are right - but if someone goes the trouble of implementing per-arch support for local increments then i'm not against it. (except if the generated code is grossly inefficient) There are architectures where cli/sti hurts alot.
In any case, on x86 we should switch to a cli/sti implementation indeed - it will quite likely have alot smaller footprint than __per_cpu_offset based approaches.
Although on x86_64 we'd probably be pretty OK if all per-cpu variables were in the PDA and were thus at a constant %gs-relative offset. But for now we only have data_offset in the PDA so there's one more unnecessary indirection.
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