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authorWill Deacon <will.deacon@arm.com>2014-11-14 11:37:34 +0100
committerRussell King <rmk+kernel@arm.linux.org.uk>2014-11-21 15:24:46 +0000
commita391263cd84e6ae2da26a54383f3abf80c18d9df (patch)
treed2bff30f0aa5a36787b9a735b081637b392003fa /arch/arm/mm
parent2b94fe2ac97fdd2ae7521004e857e33016720eb7 (diff)
ARM: 8203/1: mm: try to re-use old ASID assignments following a rollover
Rather than unconditionally allocating a fresh ASID to an mm from an older generation, attempt to re-use the old assignment where possible. This can bring performance benefits on systems where the ASID is used to tag things other than the TLB (e.g. branch prediction resources). Acked-by: Catalin Marinas <catalin.marinas@arm.com> Signed-off-by: Will Deacon <will.deacon@arm.com> Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Diffstat (limited to 'arch/arm/mm')
-rw-r--r--arch/arm/mm/context.c58
1 files changed, 34 insertions, 24 deletions
diff --git a/arch/arm/mm/context.c b/arch/arm/mm/context.c
index 6eb97b3a7481..91892569710f 100644
--- a/arch/arm/mm/context.c
+++ b/arch/arm/mm/context.c
@@ -184,36 +184,46 @@ static u64 new_context(struct mm_struct *mm, unsigned int cpu)
u64 asid = atomic64_read(&mm->context.id);
u64 generation = atomic64_read(&asid_generation);
- if (asid != 0 && is_reserved_asid(asid)) {
+ if (asid != 0) {
/*
- * Our current ASID was active during a rollover, we can
- * continue to use it and this was just a false alarm.
+ * If our current ASID was active during a rollover, we
+ * can continue to use it and this was just a false alarm.
*/
- asid = generation | (asid & ~ASID_MASK);
- } else {
+ if (is_reserved_asid(asid))
+ return generation | (asid & ~ASID_MASK);
+
/*
- * Allocate a free ASID. If we can't find one, take a
- * note of the currently active ASIDs and mark the TLBs
- * as requiring flushes. We always count from ASID #1,
- * as we reserve ASID #0 to switch via TTBR0 and to
- * avoid speculative page table walks from hitting in
- * any partial walk caches, which could be populated
- * from overlapping level-1 descriptors used to map both
- * the module area and the userspace stack.
+ * We had a valid ASID in a previous life, so try to re-use
+ * it if possible.,
*/
- asid = find_next_zero_bit(asid_map, NUM_USER_ASIDS, cur_idx);
- if (asid == NUM_USER_ASIDS) {
- generation = atomic64_add_return(ASID_FIRST_VERSION,
- &asid_generation);
- flush_context(cpu);
- asid = find_next_zero_bit(asid_map, NUM_USER_ASIDS, 1);
- }
- __set_bit(asid, asid_map);
- cur_idx = asid;
- asid |= generation;
- cpumask_clear(mm_cpumask(mm));
+ asid &= ~ASID_MASK;
+ if (!__test_and_set_bit(asid, asid_map))
+ goto bump_gen;
}
+ /*
+ * Allocate a free ASID. If we can't find one, take a note of the
+ * currently active ASIDs and mark the TLBs as requiring flushes.
+ * We always count from ASID #1, as we reserve ASID #0 to switch
+ * via TTBR0 and to avoid speculative page table walks from hitting
+ * in any partial walk caches, which could be populated from
+ * overlapping level-1 descriptors used to map both the module
+ * area and the userspace stack.
+ */
+ asid = find_next_zero_bit(asid_map, NUM_USER_ASIDS, cur_idx);
+ if (asid == NUM_USER_ASIDS) {
+ generation = atomic64_add_return(ASID_FIRST_VERSION,
+ &asid_generation);
+ flush_context(cpu);
+ asid = find_next_zero_bit(asid_map, NUM_USER_ASIDS, 1);
+ }
+
+ __set_bit(asid, asid_map);
+ cur_idx = asid;
+
+bump_gen:
+ asid |= generation;
+ cpumask_clear(mm_cpumask(mm));
return asid;
}