iommu/arm-smmu-v3: Avoid back-to-back CMD_SYNC operations

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Putting adjacent CMD_SYNCs into the command queue is nonsensical, but
can happen when multiple CPUs are inserting commands. Rather than leave
the poor old hardware to chew through these operations, we can instead
drop the subsequent SYNCs and poll for completion of the first. This
has been shown to improve IO performance under pressure, where the
number of SYNC operations reduces by about a third:

	CMD_SYNCs reduced:	19542181
	CMD_SYNCs total:	58098548	(include reduced)
	CMDs total:		116197099	(TLBI:SYNC about 1:1)

Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

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Zhen Lei 2018-08-19 15:51:11 +08:00 • committed by Will Deacon

parent 0f02477d16

commit 901510ee32

1 changed files with 13 additions and 3 deletions

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drivers/iommu/arm-smmu-v3.c

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