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

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Date:	Tue, 28 Jan 2014 13:43:10 -0500
From:	Prarit Bhargava <prarit@...hat.com>
To:	Yinghai Lu <yinghai@...nel.org>
CC:	Ingo Molnar <mingo@...e.hu>, "H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH -v2] x86, irq: get correct available vectors for cpu disable



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.  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.


... 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?

P.

> +		for (vector = FIRST_EXTERNAL_VECTOR;
> +		     vector < first_system_vector; vector++) {
> +			if (test_bit(vector, used_vectors))
> +				continue;
> +
>  			if (per_cpu(vector_irq, cpu)[vector] < 0)
>  				count++;
>  		}
--
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