Thanks for the patch.
On Tue, Jan 28, 2014 at 01:54:05PM -0800, Yinghai Lu wrote:
> used_vectors is a bitmap for vectors that are not tracked in per_cpu
> vector_irq.
I feel like this comment (also in the code) could be misleading because vectors
above first_system_vector are effectively not tracked in per_cpu vector_irq, but
also may not have the bit set in used_vectors. For example, used_vectors from a
system that I am looking at now:
first_system_vector
239 255
| |
10 01000 11111 11111
test_bit(240, used_vectors) does not return the correct answer to the question
about whether the vector is tracked in per_cpu vector_irq. This leads to two
meanings for the bitmap; for vectors less than first_system_vector whether or
not they are tracked in per_cpu vector_irq, and for vectors above
first_system_vector, whether or not they are in use:
static inline int is_per_cpu_vector(int vector) {
return !test_bit(vector, used_vectors) &&
vector < first_system_vector;
}
Thanks,
Linn
> used_vectors contains information on the first 32 exceptions, the system
> vectors.
> the IA32_SYSCALL_VECTOR (0x80), and the IRQ_MOVE_CLEANUP_VECTOR (0x20).
>
> assign_irq_vectors() assigns vectors up to first_system_vector and
> it will not use vectors that are set used_vectors.
>
> This patch modifies the code to scan up to first_system_vector
> and do a test on the used_vectors bitmap.
>
> So count avaiable vectors correctly.
>
> -v2: fix compiling problem.
> -v3: update changelog and commets
>
> Signed-off-by: Yinghai Lu <ying...@kernel.org>
>
> ---
> arch/x86/kernel/irq.c | 18 ++++++++++++++++--
> 1 file changed, 16 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 +322,21 @@ 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 scan per_cpu vectors from
> + * FIRST_EXTERNAL_VECTOR to first_system_vector.
> + * It aslo skip vectors that are set in used_vectors bitmask.
> + * used_vectors could have bits set for
> + * IA32_SYSCALL_VECTOR (0x80)
> + * IRQ_MOVE_CLEANUP_VECTOR (0x20)
> + * Don't count those as available vectors.
> + */
> + 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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