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Subject[PATCH v4 0/2] bugfix and optimization about CMD_SYNC
Date
v3->v4:
1. create a new function arm_smmu_cmdq_build_sync_msi_cmd, it's only used to
build CMD_SYNC for CS=SIG_IRQ mode.
2. In order to observe the optimization effect, I conducted 5 tests for each
case. Although the test result is volatility, but we can still get which case
is good or bad.

Test command: fio -numjobs=8 -rw=randread -runtime=30 ... -bs=4k
Test Result: IOPS

Case 1: (without these patches)
675480
672055
665275
648610
661146

Case 2: (only apply the variant of patch 1, move arm_smmu_cmdq_build_cmd into lock)
688714
697355
632951
700540
678459

Case 3: (only apply patch 1)
721582
729226
689574
679710
727770

Case 4: (apply both patch 1 and patch 2)
734077
742868
738194
682544
740586

v2 -> v3:
Although I have no data to show how many performance will be impacted
because of arm_smmu_cmdq_build_cmd is protected by spinlock. But it's
clear that the performance is bound to drop, a memset operation and
a complicate switch..case in the function arm_smmu_cmdq_build_cmd.

v1 -> v2:
1. move the call to arm_smmu_cmdq_build_cmd into the critical section,
and keep itself unchange.
2. Although patch2 can make sure no two CMD_SYNCs will be adjacent,
but patch1 is still needed, see below:

cpu0 cpu1 cpu2
msidata=0
msidata=1
insert cmd1
insert a TLBI command
insert cmd0
smmu execute cmd1
smmu execute TLBI
smmu execute cmd0
poll timeout, because msidata=1 is overridden by
cmd0, that means VAL=0, sync_idx=1.

Zhen Lei (2):
iommu/arm-smmu-v3: fix unexpected CMD_SYNC timeout
iommu/arm-smmu-v3: avoid redundant CMD_SYNCs if possible

drivers/iommu/arm-smmu-v3.c | 44 ++++++++++++++++++++++++++++++++------------
1 file changed, 32 insertions(+), 12 deletions(-)

--
1.8.3


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