linux-kernel - Re: [PATCH 0/8] tip related: radix tree for spareseirq and logical flat clean up

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Date:	Fri, 12 Feb 2010 19:44:13 -0800
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Yinghai Lu <yinghai@...nel.org>
Cc:	Ingo Molnar <mingo@...e.hu>, Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Suresh Siddha <suresh.b.siddha@...el.com>,
	linux-kernel@...r.kernel.org, Jeremy Fitzhardinge <jeremy@...p.org>
Subject: Re: [PATCH  0/8] tip related: radix tree for spareseirq and logical flat clean up

Yinghai Lu <yinghai@...nel.org> writes:

> ---------spareirq radix tree related ----------------
> 94007e8: irq: remove not need bootmem code
> 4b0d3fa: radix: move radix init early
> 56af1a9: sparseirq: change irq_desc_ptrs to static
> b236235: sparseirq: use radix_tree instead of ptrs array
> 5918787: x86: remove arch_probe_nr_irqs
>
> so could reduce nr_irqs limitation for bunch ixgbe...
>
> ---------------x86 logical flat related -----------
> f5954c4: use nr_cpus= to set nr_cpu_ids early
> 7b8d6a9: x86: use num_processors for possible cpus
> d79d1de: x86: make 32bit apic flat to physflat switch like 64bit

Thanks for keeping this work alive.

I just skimmed through do_IRQ and I happened to notice that
we have an unnecessary inefficiency that using a radix tree for
irq_to_desc will magnify.

handle_irq should take an struct irq_desc * instead of a unsigned int irq.

and the per cpu vector_irq array should become a per cpu vector_desc array.

As soon as irq_to_desc is more than &irq_desc[irq] this saves us work
and cache line misses  at the cost of a simple code cleanup.


Eric
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