Messages in this thread Patch in this message | | | From | Robin Murphy <> | Subject | [PATCH v2] iommu/iova: Try harder to allocate from rcache magazine | Date | Thu, 28 Sep 2017 11:31:23 +0100 |
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When devices with different DMA masks are using the same domain, or for PCI devices where we usually try a speculative 32-bit allocation first, there is a fair possibility that the top PFN of the rcache stack at any given time may be unsuitable for the lower limit, prompting a fallback to allocating anew from the rbtree. Consequently, we may end up artifically increasing pressure on the 32-bit IOVA space as unused IOVAs accumulate lower down in the rcache stacks, while callers with 32-bit masks also impose unnecessary rbtree overhead.
In such cases, let's try a bit harder to satisfy the allocation locally first - scanning the whole stack should still be relatively inexpensive.
Signed-off-by: Robin Murphy <robin.murphy@arm.com> ---
v2: There's no need for a 'proper' stack rotation
drivers/iommu/iova.c | 15 ++++++++++++--- 1 file changed, 12 insertions(+), 3 deletions(-)
diff --git a/drivers/iommu/iova.c b/drivers/iommu/iova.c index 506780084425..bb392fdc7a1b 100644 --- a/drivers/iommu/iova.c +++ b/drivers/iommu/iova.c @@ -822,12 +822,21 @@ static bool iova_magazine_empty(struct iova_magazine *mag) static unsigned long iova_magazine_pop(struct iova_magazine *mag, unsigned long limit_pfn) { + int i; + unsigned long pfn; + BUG_ON(iova_magazine_empty(mag)); - if (mag->pfns[mag->size - 1] > limit_pfn) - return 0; + /* Only fall back to the rbtree if we have no suitable pfns at all */ + for (i = mag->size - 1; mag->pfns[i] > limit_pfn; i--) + if (i == 0) + return 0; - return mag->pfns[--mag->size]; + /* Swap it to pop it */ + pfn = mag->pfns[i]; + mag->pfns[i] = mag->pfns[--mag->size]; + + return pfn; } static void iova_magazine_push(struct iova_magazine *mag, unsigned long pfn) -- 2.13.4.dirty
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