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Date: Tue, 20 Nov 2007 12:02:22 -0500 From: Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca> To: Rusty Russell <rusty@...tcorp.com.au> Cc: akpm@...ux-foundation.org, linux-kernel@...r.kernel.org, Andi Kleen <ak@....de>, "H. Peter Anvin" <hpa@...or.com>, Chuck Ebbert <cebbert@...hat.com>, Christoph Hellwig <hch@...radead.org>, Jeremy Fitzhardinge <jeremy@...p.org>, Ingo Molnar <mingo@...hat.com>, Thomas Gleixner <tglx@...utronix.de> Subject: Re: [patch 5/8] Immediate Values - x86 Optimization (simplified) * Rusty Russell (rusty@...tcorp.com.au) wrote: > On Tuesday 20 November 2007 01:28:03 Mathieu Desnoyers wrote: > > * Rusty Russell (rusty@...tcorp.com.au) wrote: > > > I think it would be easier to just fast-path the num_online_cpus == 1 > > > case, even if you want to keep this "update_early" interface. > > > > Nope, that could lead to problems. I call core_immediate_update() > > _very_ early, before boot_cpu_init() is called. > > Ah, I see the problem. It would in fact be clearer for us to move > boot_cpu_init() up to just after smp_setup_processor_id() in start_kernel > anyway, not just for this code, but in general. > Could be done. > > Therefore, > > cpu_online_map is not set yet. I am not sure the benefit of using > > num_online_cpus outweights the added fragility wrt other boot process > > initializations. > > I think it's still a win, though worth a comment that we always go via the > non-IPI path for the early boot case. > Ok, another potential problem then : If we fast-path the num_online_cpus == 1, then updates done after the boot process will have to go through this code. Therefore, we would have to disable interrupts in the early boot code. However, I doubt it is safe to use the paravirtualized local_irq_disable/enable before the paravirt code is executed ? Mathieu > Cheers, > Rusty. -- Mathieu Desnoyers Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68 - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.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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