On 2020-12-13 16:32, Heiner Kallweit wrote:
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.
Reviewed-by: Robin Murphy <robin.mur...@arm.com>
FWIW I consider this case similar to the same hint in WARN_ON() and
friends - it's a pretty severe condition that should never be expected
to be hit in normal operation, so it's entirely logical for it to be
implicitly unlikely. I struggle to imagine any case that would
specifically *not* want that (or worse, want to hint it as likely). Some
DMA API backends may spend considerable time trying as hard as possible
to make a mapping work before eventually admitting defeat, so the idea
of ever trying to optimise at the driver level for failure in hot paths
just makes no sense.
Thanks,
Robin.
Signed-off-by: Heiner Kallweit <hkallwe...@gmail.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;
