linux-kernel - [PATCH v2] dma-mapping: add unlikely hint for error path in dma_mapping

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Message-ID: <39581f9a-0066-ad98-094d-d41082145e23@gmail.com>
Date:   Sun, 13 Dec 2020 17:32:39 +0100
From:   Heiner Kallweit <hkallweit1@...il.com>
To:     Christoph Hellwig <hch@....de>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Robin Murphy <robin.murphy@....com>,
        Barry Song <song.bao.hua@...ilicon.com>
Cc:     "open list:AMD IOMMU (AMD-VI)" <iommu@...ts.linux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: [PATCH v2] dma-mapping: add unlikely hint for error path in
 dma_mapping_error

Zillions of drivers use the unlikely() hint when checking the result of
dma_mapping_error(). This is an inline function anyway, so we can move
the hint into this function and remove it from drivers.

Signed-off-by: Heiner Kallweit <hkallweit1@...il.com>
---
v2:
Split the big patch into the change for dma-mapping.h and follow-up
patches per subsystem that will go through the trees of the respective
maintainers.
---
 include/linux/dma-mapping.h | 2 +-
 kernel/dma/map_benchmark.c  | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h
index 2e49996a8..6177e20b5 100644
--- a/include/linux/dma-mapping.h
+++ b/include/linux/dma-mapping.h
@@ -95,7 +95,7 @@ static inline int dma_mapping_error(struct device *dev, dma_addr_t dma_addr)
 {
 	debug_dma_mapping_error(dev, dma_addr);
 
-	if (dma_addr == DMA_MAPPING_ERROR)
+	if (unlikely(dma_addr == DMA_MAPPING_ERROR))
 		return -ENOMEM;
 	return 0;
 }
diff --git a/kernel/dma/map_benchmark.c b/kernel/dma/map_benchmark.c
index b1496e744..901420a5d 100644
--- a/kernel/dma/map_benchmark.c
+++ b/kernel/dma/map_benchmark.c
@@ -78,7 +78,7 @@ static int map_benchmark_thread(void *data)
 
 		map_stime = ktime_get();
 		dma_addr = dma_map_single(map->dev, buf, PAGE_SIZE, map->dir);
-		if (unlikely(dma_mapping_error(map->dev, dma_addr))) {
+		if (dma_mapping_error(map->dev, dma_addr)) {
 			pr_err("dma_map_single failed on %s\n",
 				dev_name(map->dev));
 			ret = -ENOMEM;
-- 
2.29.2