On 14.12.2020 14:01, Robin Murphy wrote:
> 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;
>>
Is this patch going to make it to linux-next?
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