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

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Date:	Sat, 13 Feb 2010 04:04:10 -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>,
	Rusty Russell <rusty@...tcorp.com.au>
Subject: Re: [PATCH  0/8] tip related: radix tree for spareseirq and logical flat clean up

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

> On 02/12/2010 07:44 PM, Eric W. Biederman wrote:
>> 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.
>> 
>
> please check
>
> Subject: [PATCH] x86: use vector_desc instead of vector_irq
>
> Eric pointed out that radix tree version of irq_to_desc will magnify delay on the path
> of handle_irq.
> use vector_desc to reduce the calling of irq_to_desc.
>
> next step: need to change all ack, mask, umask, eoi for all irq_chip to take irq_desc
>
> Signed-off-by: Yinghai Lu <yinghai@...nel.org>
>  
>  #ifdef CONFIG_X86_LOCAL_APIC
> Index: linux-2.6/arch/x86/lguest/boot.c
> ===================================================================
> --- linux-2.6.orig/arch/x86/lguest/boot.c
> +++ linux-2.6/arch/x86/lguest/boot.c
> @@ -819,7 +819,7 @@ static void __init lguest_init_IRQ(void)
>  
>  	for (i = FIRST_EXTERNAL_VECTOR; i < NR_VECTORS; i++) {
>  		/* Some systems map "vectors" to interrupts weirdly.  Not us! */
> -		__get_cpu_var(vector_irq)[i] = i - FIRST_EXTERNAL_VECTOR;
> +		__get_cpu_var(vector_desc)[i] = irq_to_desc(i - FIRST_EXTERNAL_VECTOR);
>  		if (i != SYSCALL_VECTOR)
>  			set_intr_gate(i, interrupt[i - FIRST_EXTERNAL_VECTOR]);
>  	}

YH It appears that irq_to_desc_alloc_node has not been called yet
so the setting of vector_desc needs to move to lguest_setup_irq.

Eric



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