linux-kernel - [PATCH v2 2/2] swiotlb: checking whether swiotlb buffer is full with io_tlb

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Date:   Mon, 10 Dec 2018 08:37:58 +0800
From:   Dongli Zhang <dongli.zhang@...cle.com>
To:     iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Cc:     konrad.wilk@...cle.com, hch@....de, m.szyprowski@...sung.com,
        robin.murphy@....com, joe.jin@...cle.com, dongli.zhang@...cle.com
Subject: [PATCH v2 2/2] swiotlb: checking whether swiotlb buffer is full with io_tlb_used

This patch uses io_tlb_used to help check whether swiotlb buffer is full.
io_tlb_used is no longer used for only debugfs. It is also used to help
optimize swiotlb_tbl_map_single().

Suggested-by: Joe Jin <joe.jin@...cle.com>
Signed-off-by: Dongli Zhang <dongli.zhang@...cle.com>
---
 kernel/dma/swiotlb.c | 10 ++++------
 1 file changed, 4 insertions(+), 6 deletions(-)

diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
index 3979c2c..9300341 100644
--- a/kernel/dma/swiotlb.c
+++ b/kernel/dma/swiotlb.c
@@ -76,12 +76,10 @@ static phys_addr_t io_tlb_start, io_tlb_end;
  */
 static unsigned long io_tlb_nslabs;
 
-#ifdef CONFIG_DEBUG_FS
 /*
  * The number of used IO TLB block
  */
 static unsigned long io_tlb_used;
-#endif
 
 /*
  * This is a free list describing the number of free entries available from
@@ -489,6 +487,10 @@ phys_addr_t swiotlb_tbl_map_single(struct device *hwdev,
 	 * request and allocate a buffer from that IO TLB pool.
 	 */
 	spin_lock_irqsave(&io_tlb_lock, flags);
+
+	if (unlikely(nslots > io_tlb_nslabs - io_tlb_used))
+		goto not_found;
+
 	index = ALIGN(io_tlb_index, stride);
 	if (index >= io_tlb_nslabs)
 		index = 0;
@@ -538,9 +540,7 @@ phys_addr_t swiotlb_tbl_map_single(struct device *hwdev,
 		dev_warn(hwdev, "swiotlb buffer is full (sz: %zd bytes)\n", size);
 	return SWIOTLB_MAP_ERROR;
 found:
-#ifdef CONFIG_DEBUG_FS
 	io_tlb_used += nslots;
-#endif
 	spin_unlock_irqrestore(&io_tlb_lock, flags);
 
 	/*
@@ -602,9 +602,7 @@ void swiotlb_tbl_unmap_single(struct device *hwdev, phys_addr_t tlb_addr,
 		for (i = index - 1; (OFFSET(i, IO_TLB_SEGSIZE) != IO_TLB_SEGSIZE -1) && io_tlb_list[i]; i--)
 			io_tlb_list[i] = ++count;
 
-#ifdef CONFIG_DEBUG_FS
 		io_tlb_used -= nslots;
-#endif
 	}
 	spin_unlock_irqrestore(&io_tlb_lock, flags);
 }
-- 
2.7.4