Messages in this thread | | | Date | Wed, 9 Aug 2023 14:50:13 +0100 | From | Will Deacon <> | Subject | Re: [PATCH v5 8/9] iommu/arm-smmu-v3: Skip cd sync if CD table isn't active |
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On Wed, Aug 09, 2023 at 01:12:04AM +0800, Michael Shavit wrote: > This commit explicitly keeps track of whether a CD table is installed in > an STE so that arm_smmu_sync_cd can skip the sync when unnecessary. This > was previously achieved through the domain->devices list, but we are > moving to a model where arm_smmu_sync_cd directly operates on a master > and the master's CD table instead of a domain.
Why is this path worth optimising?
> 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 f5ad386cc8760..488d12dd2d4aa 100644 > --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c > +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c > @@ -985,6 +985,9 @@ static void arm_smmu_sync_cd(struct arm_smmu_master *master, > }, > }; > > + if (!master->cd_table.installed) > + return;
Doesn't this interact badly with the sync in arm_smmu_detach_dev(), which I think happens after zapping the STE?
> cmds.num = 0; > for (i = 0; i < master->num_streams; i++) { > cmd.cfgi.sid = master->streams[i].id; > @@ -1091,7 +1094,7 @@ int arm_smmu_write_ctx_desc(struct arm_smmu_master *master, int ssid, > cdptr[3] = cpu_to_le64(cd->mair); > > /* > - * STE is live, and the SMMU might read dwords of this CD in any > + * STE may be live, and the SMMU might read dwords of this CD in any > * order. Ensure that it observes valid values before reading > * V=1. > */
Why does this patch need to update this comment?
Will
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