linux-kernel - Re: [PATCH 00/16] dyn_array and nr

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Message-ID: <86802c440808011430i6cf5cb8cn519777a78dd987b0@mail.gmail.com>
Date:	Fri, 1 Aug 2008 14:30:55 -0700
From:	"Yinghai Lu" <yhlu.kernel@...il.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	"Ingo Molnar" <mingo@...e.hu>,
	"Thomas Gleixner" <tglx@...utronix.de>, hpa <hpa@...or.com>,
	"Dhaval Giani" <dhaval@...ux.vnet.ibm.com>,
	"Mike Travis" <travis@....com>,
	"Andrew Morton" <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 00/16] dyn_array and nr_irqs support v2

On Fri, Aug 1, 2008 at 1:46 PM, Eric W. Biederman <ebiederm@...ssion.com> wrote:
> Yinghai Lu <yhlu.kernel@...il.com> writes:
>
>> Please check dyn_array support for x86
>
> YH you have not addressed any of my core concerns and this exceeds my review limit.

i mean drivers/serial/8250.c

> Unfortunately I don't feel like this is a productive process.
>
> My core concerns are:
> - You have not separated out and separately pushed the regression patch.  So that we can
>  fix the current rc release.  Simply tuning NR_IRQS is all I feel comfortable with for
>  fixing things in the post merge window period.

Increase NR_IRQS to 512 for x86_64?

>
> - The generic code has no business with dealing with NR_IRQS sized arrays.
>  Since we don't have a generic problem I don't see why we should have a generic dyn_array solution.
besides

arch/x86/kernel/io_apic_32.c:DEFINE_DYN_ARRAY(irq_2_pin, sizeof(struct
irq_pin_list), pin_map_size, 16, NULL);
arch/x86/kernel/io_apic_32.c:DEFINE_DYN_ARRAY(balance_irq_affinity,
sizeof(struct balance_irq_affinity), nr_irqs, PAGE_SIZE,
irq_affinity_init_work);
arch/x86/kernel/io_apic_32.c:DEFINE_DYN_ARRAY(irq_vector, sizeof(u8),
nr_irqs, PAGE_SIZE, irq_vector_init_work);
arch/x86/kernel/io_apic_64.c:DEFINE_DYN_ARRAY(irq_cfg, sizeof(struct
irq_cfg), nr_irqs, PAGE_SIZE, init_work);
arch/x86/kernel/io_apic_64.c:DEFINE_DYN_ARRAY(irq_2_pin, sizeof(struct
irq_pin_list), pin_map_size, sizeof(struct irq_pin_list), NULL);

kernel/sched.c:DEFINE_PER_CPU_DYN_ARRAY_ADDR(per_cpu__kstat_irqs,
per_cpu__kstat.irqs, sizeof(unsigned int), nr_irqs, sizeof(unsigned
long), NULL);

and kstat.irqs is the killer... every cpu will have that. [NR_CPUS][NR_IRQS]...

>
> - The dyn_array infrastructure does not provide for per numa node allocation of
>  irq_desc structures, limiting NUMA scalability.

you plan to move irq_desc when irq_affinity is set to cpus on other node?

something like DEFINE_PER_NODE_DYN_ARRAY ?

>
> - You appear to be papering over problems instead of digging in and actually fixing them.

use dyn_array is less intrusive at this point. and dyn_array related
code is not big.
just NR_IRQS to nr_irqs to make the patches more bigger. actually it is simple.

with acpi_madt probing, nr_irqs is much small. like 48 or 98. and
current one is MACRO 224 or 256.

>
> YH  Here is what I was suggesting when the topic of killing NR_IRQs came up a week or so
> ago.
> http://lkml.org/lkml/2008/7/10/439
> http://lkml.org/lkml/2008/7/10/532
>
> Which essentially boils down to:
> - Removing NR_IRQS from the non-irq infrastructure code.
> - Add a config option for architectures that are not going to use an array
> - In the genirq code have a lookup function that goes from irq number to irq_desc *.

so we need one pointer array with that lookup function? what is the
pointer array index size?
or use list in that lookup function?

how about percpu kstat.irqs?

>
> The rest we should be able to handle in a arch dependent fashion.
>
> When we are done we should be able to create a stable irq number for msi interrupts
> that is something like:  bus:dev:fun:vector_no which is 8+5+3+12=28 bits long.

how about irq migration from one cpu to another with different vector_no ?

YH
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