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Commit ea943966 authored by H. Peter Anvin's avatar H. Peter Anvin
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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: default avatarH. Peter Anvin <hpa@zytor.com>
LKML-Reference: <4B426550.6000209@kernel.org>
parent 99d113b1

arch/x86/include/asm/irq_vectors.h

+5 −4
Original line number Diff line number Diff line
@@ -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

arch/x86/kernel/apic/io_apic.c

+2 −1
Original line number Diff line number Diff line
@@ -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;