x86, apic: Don't waste a vector to improve vector spread

We want to use a vector-assignment sequence that avoids stumbling onto
0x80 earlier in the sequence, in order to improve the spread of
vectors across priority levels on machines with a small number of
interrupt sources.  Right now, this is done by simply making the first
vector (0x31 or 0x41) completely unusable.  This is unnecessary; all
we need is to start assignment at a +1 offset, we don't actually need
to prohibit the usage of this vector once we have wrapped around.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>
LKML-Reference: <4B426550.6000209@kernel.org>

1 files changed, 2 insertions, 1 deletions

diff --git a/arch/x86/kernel/apic/io_apic.c b/arch/x86/kernel/apic/io_apic.c
index d9cd1f1b9c07..e9ba0903e9d5 100644
--- a/arch/x86/kernel/apic/io_apic.c
+++ b/arch/x86/kernel/apic/io_apic.c
@@ -1162,7 +1162,8 @@ __assign_irq_vector(int irq, struct irq_cfg *cfg, const struct cpumask *mask)
          * Also, we've got to be careful not to trash gate
          * 0x80, because int 0x80 is hm, kind of importantish. ;)
          */
-        static int current_vector = FIRST_DEVICE_VECTOR, current_offset = 0;
+        static int current_vector = FIRST_DEVICE_VECTOR + VECTOR_OFFSET_START;
+        static int current_offset = VECTOR_OFFSET_START % 8;
         unsigned int old_vector;
         int cpu, err;
         cpumask_var_t tmp_mask;