Messages in this thread | | | Date | Mon, 14 Nov 2022 10:46:47 +0000 | Subject | Re: [PATCH] iommu/arm-smmu-v3: Optimize checking for invalid values | From | Robin Murphy <> |
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On 2022-11-13 13:38, Harry Song wrote: > Move the check of invalid value (iotlb_gather->pgsize = 0) from > arm_smmu_iotlb_sync() to __arm_smmu_tlb_inv_range() for iotlb sync > to make the code clearer.
How is this an optimisation? It adds a redundant check on paths that don't need it, and even the unmap error paths now have to do *more* work to figure out when there's nothing to sync. Furthermore, to me "clear code" means making decisions at the appropriate level of abstraction, not deliberately passing invalid arguments down through 3 more levels of callstack to eventually do nothing.
If you think that the gather->pgsize logic is hard to follow and needs more explanation then by all means add a comment to call out how iommu_iotlb_gather_init() and iommu_iotlb_gather_add_page() join it up, but I don't agree with this patch as it is, sorry.
Thanks, Robin.
> Signed-off-by: Harry Song <jundongsong1@gmail.com> > --- > drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 5 +---- > 1 file changed, 1 insertion(+), 4 deletions(-) > > diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c > index 6d5df91c5..e51b9f506 100644 > --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c > +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c > @@ -1873,7 +1873,7 @@ static void __arm_smmu_tlb_inv_range(struct arm_smmu_cmdq_ent *cmd, > size_t inv_range = granule; > struct arm_smmu_cmdq_batch cmds; > > - if (!size) > + if (!size || !inv_range) > return; > > if (smmu->features & ARM_SMMU_FEAT_RANGE_INV) { > @@ -2507,9 +2507,6 @@ static void arm_smmu_iotlb_sync(struct iommu_domain *domain, > { > struct arm_smmu_domain *smmu_domain = to_smmu_domain(domain); > > - if (!gather->pgsize) > - return; > - > arm_smmu_tlb_inv_range_domain(gather->start, > gather->end - gather->start + 1, > gather->pgsize, true, smmu_domain);
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