linux-kernel - Re: [PATCH -v2] x86, irq: get correct available vectors for cpu disable

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Date:	Tue, 28 Jan 2014 13:47:27 -0800
From:	Yinghai Lu <yinghai@...nel.org>
To:	Prarit Bhargava <prarit@...hat.com>
Cc:	Ingo Molnar <mingo@...e.hu>, "H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH -v2] x86, irq: get correct available vectors for cpu disable

On Tue, Jan 28, 2014 at 10:43 AM, Prarit Bhargava <prarit@...hat.com> wrote:
>
>
> On 01/26/2014 03:50 PM, Yinghai Lu wrote:
>> assign_irq_vector will stop before first_system_vector.
>> also it will not vector that is set in used_vectors.
>>
>> used_vectors is used to track non per_cpu irq_vector in vector_irq.
>> It include first 32 exception [0,1f) and system vector near 0xfe.
>> and IA32_SYSCALL_VECTOR (0x80), IRQ_MOVE_CLEANUP_VECTOR (0x20).
>>
>> So add checking for them for counting avaiable vectors.
>>
>
> Yinghai, no objection to the patch ... but how about
>
>
> used_vectors is a bitmap for global irqs; it tracks the non per_cpu
> irq_vectors in vector_irq.  used_vectors contains information on the first 32
> exceptions (0 to 0x1f), the system vectors near the first system vector
> (0xfe), the IA32_SYSCALL_VECTOR (0x80), and the IRQ_MOVE_CLEANUP_VECTOR (0x20)
>
> assign_irq_vectors() assigns vectors up to first_system_vector (0xfe) and
> sets the used_vectors bit for each assigned vector.

No, assign_irq_vectors will not touch used_vectors.

>  Currently, the
> IRQ checking code only scans from the FIRST_EXTERNAL_VECTOR to the end of
> the vectors.  This patch modifies the code to scan to first_system_vector
> and do a test on the used_vectors bitmap.

first_system_vector start from 0xfe, and will be updated ....would end up with
0xf7.

>
>
> ... and ...
>
>> -v2: fix compiling problem.
>>
>> Signed-off-by: Yinghai Lu <yinghai@...nel.org>
>>
>> ---
>>  arch/x86/kernel/irq.c |   16 ++++++++++++++--
>>  1 file changed, 14 insertions(+), 2 deletions(-)
>>
>> Index: linux-2.6/arch/x86/kernel/irq.c
>> ===================================================================
>> --- linux-2.6.orig/arch/x86/kernel/irq.c
>> +++ linux-2.6/arch/x86/kernel/irq.c
>> @@ -17,6 +17,7 @@
>>  #include <asm/idle.h>
>>  #include <asm/mce.h>
>>  #include <asm/hw_irq.h>
>> +#include <asm/desc.h>
>>
>>  #define CREATE_TRACE_POINTS
>>  #include <asm/trace/irq_vectors.h>
>> @@ -321,8 +322,19 @@ int check_irq_vectors_for_cpu_disable(vo
>>       for_each_online_cpu(cpu) {
>>               if (cpu == this_cpu)
>>                       continue;
>> -             for (vector = FIRST_EXTERNAL_VECTOR; vector < NR_VECTORS;
>> -                  vector++) {
>> +
>> +             /*
>> +              * assign_irq_vector() only use vector under
>> +              * first_system_vector and not set in used_vectors bitmask.
>> +              * used_vectors could have bits set for
>> +              *      IA32_SYSCALL_VECTOR (0x80)
>> +              *      IRQ_MOVE_CLEANUP_VECTOR (0x20)
>> +              */
>
>
> +               /*
> +                * assign_irq_vector() will only scan non per_cpu vectors from
> +                * FIRST_EXTERNAL_VECTOR to first_system_vector (0xfe) and not
> +                * set in used_vectors bitmask.  This takes into account
> +                * the IA32_SYSCALL_VECTOR and the IRQ_MOVE_CLEANUP_VECTOR,
> +                * which should not be counted.
> +                */
>
> ... what do you think?
>

will send updated version.

Thanks

Yinghai
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