Messages in this thread | | | Date | Thu, 13 Apr 2023 11:16:22 +0100 | Subject | Re: [PATCH v3] iommu: Optimise PCI SAC address trick | From | John Garry <> |
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On 20/01/2023 11:33, John Garry wrote: > On 18/01/2023 17:26, Robin Murphy wrote: >> Per the reasoning in commit 4bf7fda4dce2 ("iommu/dma: Add config for >> PCI SAC address trick") and its subsequent revert, this mechanism no >> longer serves its original purpose, but now only works around broken >> hardware/drivers in a way that is unfortunately too impactful to remove. >> >> This does not, however prevent us from solving the performance impact >> which the workaround imposes on large-scale systems that don't need it. >> That is felt once the 32-bit IOVA space fills up and we keep >> unsuccessfully trying to allocate from it. However, if we get to that >> point then in fact it's already the endgame. The nature of the allocator >> is such that the first IOVA we give to a device after the 32-bit space >> runs out will be the highest possible address for that device, ever. >> If that works, then great, we can be pretty sure it's safe to optimise >> for speed by always allocating from the full range. And if it doesn't, >> then the worst has already happened and any brokenness is now showing, >> so there's no point continuing to try to hide it. >> >> To that end, implement a flag to refine this into a per-device policy >> that can automatically get itself out of the way if and when it stops >> being useful. >> >> CC: John Garry <john.garry@huawei.com> >> CC: Linus Torvalds <torvalds@linux-foundation.org> >> Signed-off-by: Robin Murphy <robin.murphy@arm.com> >> --- >> >> v3: Expand the flag name, add a print with inline commentary for good >> measure, and refactor the code flow even more (too many ifs and >> indents...) such that I didn't presume to carry forward John's R-b. > > I like the new changes, so feel free to add: > > Reviewed-by: John Garry <john.g.garry@oracle.com>
Is there any chance that this can be picked up?
I also saw that it fixed an issue for Jakub (cc'ed) recently.
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