Messages in this thread | | | Date | Mon, 19 Nov 2007 09:28:03 -0500 | From | Mathieu Desnoyers <> | Subject | Re: [patch 5/8] Immediate Values - x86 Optimization (simplified) |
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* Rusty Russell (rusty@rustcorp.com.au) wrote: > On Saturday 17 November 2007 01:03:35 Mathieu Desnoyers wrote: > > x86 optimization of the immediate values which uses a movl with code > > patching to set/unset the value used to populate the register used as > > variable source. > > Since immediate values are by definition an optimization, I think it makes > sense to insist they be 1, 2, 4 or 8 bytes. A BUILD_BUG_ON() in the right > place should ensure this (probably in generic code rather than x86). > sure,
> > =================================================================== > > --- linux-2.6-lttng.orig/arch/x86/kernel/traps_32.c > > I don't think you need any modification to this file now. > yep,
> > + * Create the instruction in a discarded section to calculate its size. This is > > + * how we can align the beginning of the instruction on an address that will > > + * permit atomic modificatino of the immediate value without knowing the size of > > + * the opcode used by the compiler. The operand size is known in advance. > > + */ > > This alignment is also now unnecessary. >
right,
> > +++ linux-2.6-lttng/arch/x86/kernel/immediate.c 2007-11-16 > > 08:56:22.000000000 -0500 @@ -0,0 +1,143 @@ > > +/* > > + * Immediate Value - x86 architecture specific code. > > This is now almost entirely generic code, but I suppose we can let the next > architecture hoist it out. >
I'll move it to kernel/immediate.c. We can therefore remove the powerpc immediate.c as well.
> > +/** > > + * arch_immediate_update_early - update one immediate value at boot time > > + * @immediate: pointer of type const struct __immediate to update > > + * > > + * Update one immediate value at boot time. > > + */ > > +void arch_immediate_update_early(const struct __immediate *immediate) > > 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. 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.
> But I like your IPI algorithm: very tight. >
Thanks. Many thanks for the review, I'll repost the patchset for comments.
Mathieu
-- 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@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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