Re: [PATCH] Documentation DMA-API-HOWTO.txt Add dma mapping errorcheck usage examples

From: Michael Kerrisk (man-pages)
Date: Thu Oct 18 2012 - 06:13:34 EST

On Thu, Oct 18, 2012 at 11:47 AM, Dan Carpenter
<dan.carpenter@xxxxxxxxxx> wrote:
> On Sun, Oct 14, 2012 at 09:54:24AM -0600, Shuah Khan wrote:
>> diff --git a/Documentation/DMA-API-HOWTO.txt b/Documentation/DMA-API-HOWTO.txt
>> index a0b6250..cf1adb4 100644
>> --- a/Documentation/DMA-API-HOWTO.txt
>> +++ b/Documentation/DMA-API-HOWTO.txt
>> @@ -468,11 +468,46 @@ To map a single region, you do:
>> size_t size = buffer->len;
>> dma_handle = dma_map_single(dev, addr, size, direction);
>> + if (unlikely(dma_mapping_error(dma_handle))) {
> Don't encourage people to put unlikely() and likely() into their
> driver code. It should only be used after benchmarking both with
> and without. I can't imagine how it would make a measurable
> difference here.

(Hi Dan)

Quite. See

I wonder how many blind uses of likely() and unlikely() in the kernel
are actually degrading performance.



Michael Kerrisk
Linux man-pages maintainer;
Author of "The Linux Programming Interface";
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