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

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Message-ID: <4B772A54.1000000@kernel.org>
Date:	Sat, 13 Feb 2010 14:40:20 -0800
From:	Yinghai Lu <yinghai@...nel.org>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Rusty Russell <rusty@...tcorp.com.au>
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

On 02/13/2010 04:04 AM, Eric W. Biederman wrote:
> 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.

lguest is using sparseirq?

YH
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