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As a side effect, READ_ONCE() also enforces strict types and > may add an extra instruction. But it should not have negative > performance impact since we use cpu_relax anyway and the extra time(by > adding an instruction) may allow IOMMU HW request cacheline ownership easier. > > e.g. gcc 12.3 > BEFORE: > 81 38 ad de 00 00 cmpl $0x2,(%rax) > > AFTER (with READ_ONCE()) > 772f: 8b 00 mov (%rax),%eax > 7731: 3d ad de 00 00 cmp $0x2,%eax //status data is 32 bit > > Signed-off-by: Jacob Pan > --- > drivers/iommu/intel/dmar.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/iommu/intel/dmar.c b/drivers/iommu/intel/dmar.c > index 304e84949ca7..1c8d3141cb55 100644 > --- a/drivers/iommu/intel/dmar.c > +++ b/drivers/iommu/intel/dmar.c > @@ -1446,7 +1446,7 @@ int qi_submit_sync(struct intel_iommu *iommu, struct qi_desc *desc, > */ > writel(qi->free_head << shift, iommu->reg + DMAR_IQT_REG); > > - while (qi->desc_status[wait_index] != QI_DONE) { > + while (READ_ONCE(qi->desc_status[wait_index]) != QI_DONE) { > /* > * We will leave the interrupts disabled, to prevent interrupt > * context to queue another cmd while a cmd is already submitted Reviewed-by: Yi Liu -- Regards, Yi Liu