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ARM: 8203/1: mm: try to re-use old ASID assignments following a rollover

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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>
This commit is contained in:
Will Deacon 2014-11-14 11:37:34 +01:00 committed by Russell King
parent 2b94fe2ac9
commit a391263cd8
1 changed files with 34 additions and 24 deletions
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40
arch/arm/mm/context.c
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@ -184,22 +184,31 @@ 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 &= ~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) {
@ -208,12 +217,13 @@ static u64 new_context(struct mm_struct *mm, unsigned int cpu)
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;
}