On (03/23/15 12:29), David Miller wrote: > > In order to elide the IOMMU flush as much as possible, I implemnented > a scheme for sun4u wherein we always allocated from low IOMMU > addresses to high IOMMU addresses. > > In this regime, we only need to flush the IOMMU when we rolled over > back to low IOMMU addresses during an allocation. > > It made a noticable difference in performance. > > Unfortunately, with sun4v and the hypervisor, I'm not allowed to > control when the IOMMU flush happens, it has to occur on every > single IOMMU mapping change. So this optimization was no longer > possible there. > > Anyways, that's the history behind it. > -- I see. If it was only an optimization (i.e., removing it would not break any functionality), and if this was done for older hardware, and *if* we believe that the direction of most architectures is to follow the sun4v/HV model, then, given that the sun4u code only uses 1 arena pool anyway, one thought that I have for refactoring this is the following: - Caller of iommu_tbl_range_alloc() can do the flush_all if they see start <= end for the one single pool - lose the other ->flush_all invocation (i.e., the one that is done when iommu_area_alloc() fails for pass == 0, and we reset start to 0 to roll-back) that would avoid the need for any iommu_tbl_ops in my patch-set. But it would imply that you would still take the perf hit for the roll-back if we failed the pass == 0 iteration through iommu_area_alloc(). Perhaps this is an acceptable compromise in favor of cleaner code (again, assuming that current/future archs will all follow the HV based design). --Sowmini -- To unsubscribe from this list: send the line "unsubscribe sparclinux" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
