linux-kernel - [PATCH] iommu/iova: Optimise attempts to allocate iova from 32bit address range

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Date:   Tue,  7 Aug 2018 14:24:37 +0530
From:   Ganapatrao Kulkarni <ganapatrao.kulkarni@...ium.com>
To:     joro@...tes.org, iommu@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org, robin.murphy@....com
Cc:     tomasz.nowicki@...ium.com, jnair@...iumnetworks.com,
        Robert.Richter@...ium.com, Vadim.Lomovtsev@...ium.com,
        Jan.Glauber@...ium.com, gklkml16@...il.com
Subject: [PATCH] iommu/iova: Optimise attempts to allocate iova from 32bit address range

As an optimisation for PCI devices, there is always first attempt
been made to allocate iova from SAC address range. This will lead
to unnecessary attempts/function calls, when there are no free ranges
available.

This patch optimises by adding flag to track previous failed attempts
and avoids further attempts until replenish happens.

Signed-off-by: Ganapatrao Kulkarni <ganapatrao.kulkarni@...ium.com>
---
This patch is based on comments from Robin Murphy <robin.murphy@....com>
for patch [1]

[1] https://lkml.org/lkml/2018/4/19/780

 drivers/iommu/iova.c | 11 ++++++++++-
 include/linux/iova.h |  1 +
 2 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/drivers/iommu/iova.c b/drivers/iommu/iova.c
index 83fe262..d97bb5a 100644
--- a/drivers/iommu/iova.c
+++ b/drivers/iommu/iova.c
@@ -56,6 +56,7 @@ init_iova_domain(struct iova_domain *iovad, unsigned long granule,
 	iovad->granule = granule;
 	iovad->start_pfn = start_pfn;
 	iovad->dma_32bit_pfn = 1UL << (32 - iova_shift(iovad));
+	iovad->free_32bit_pfns = true;
 	iovad->flush_cb = NULL;
 	iovad->fq = NULL;
 	iovad->anchor.pfn_lo = iovad->anchor.pfn_hi = IOVA_ANCHOR;
@@ -139,8 +140,10 @@ __cached_rbnode_delete_update(struct iova_domain *iovad, struct iova *free)
 
 	cached_iova = rb_entry(iovad->cached32_node, struct iova, node);
 	if (free->pfn_hi < iovad->dma_32bit_pfn &&
-	    free->pfn_lo >= cached_iova->pfn_lo)
+	    free->pfn_lo >= cached_iova->pfn_lo) {
 		iovad->cached32_node = rb_next(&free->node);
+		iovad->free_32bit_pfns = true;
+	}
 
 	cached_iova = rb_entry(iovad->cached_node, struct iova, node);
 	if (free->pfn_lo >= cached_iova->pfn_lo)
@@ -290,6 +293,10 @@ alloc_iova(struct iova_domain *iovad, unsigned long size,
 	struct iova *new_iova;
 	int ret;
 
+	if (limit_pfn <= iovad->dma_32bit_pfn &&
+			!iovad->free_32bit_pfns)
+		return NULL;
+
 	new_iova = alloc_iova_mem();
 	if (!new_iova)
 		return NULL;
@@ -299,6 +306,8 @@ alloc_iova(struct iova_domain *iovad, unsigned long size,
 
 	if (ret) {
 		free_iova_mem(new_iova);
+		if (limit_pfn <= iovad->dma_32bit_pfn)
+			iovad->free_32bit_pfns = false;
 		return NULL;
 	}
 
diff --git a/include/linux/iova.h b/include/linux/iova.h
index 928442d..3810ba9 100644
--- a/include/linux/iova.h
+++ b/include/linux/iova.h
@@ -96,6 +96,7 @@ struct iova_domain {
 						   flush-queues */
 	atomic_t fq_timer_on;			/* 1 when timer is active, 0
 						   when not */
+	bool	free_32bit_pfns;
 };
 
 static inline unsigned long iova_size(struct iova *iova)
-- 
2.9.4