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

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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>
This commit is contained in:
H. Peter Anvin 2010-01-04 21:14:41 -08:00
parent 99d113b17e
commit ea94396629
2 changed files with 7 additions and 5 deletions
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9
arch/x86/include/asm/irq_vectors.h
View File

@ -133,11 +133,12 @@
#define MCE_SELF_VECTOR 0xeb
/*
* First APIC vector available to drivers: (vectors 0x30-0xee) we
* start at 0x31 to spread out vectors evenly between priority
* levels. (0x80 is the syscall vector)
* First APIC vector available to drivers: (vectors 0x30-0xee). We
* start allocating at 0x31 to spread out vectors evenly between
* priority levels. (0x80 is the syscall vector)
*/
#define FIRST_DEVICE_VECTOR (IRQ15_VECTOR + 2)
#define FIRST_DEVICE_VECTOR (IRQ15_VECTOR + 1)
#define VECTOR_OFFSET_START 1
#define NR_VECTORS 256

3
arch/x86/kernel/apic/io_apic.c
View File

@ -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;