Re: [Linux-nvdimm] [PATCH 4/6] SQUSHME: pmem: Micro cleaning

[Dan Williams]

On Tue, Mar 31, 2015 at 8:24 AM, Boaz Harrosh <boaz@xxxxxxxxxxxxx> wrote:
> On 03/31/2015 06:17 PM, Dan Williams wrote:
>> On Tue, Mar 31, 2015 at 6:27 AM, Boaz Harrosh <boaz@xxxxxxxxxxxxx> wrote:
>>>
>>> Some error checks had unlikely some did not. Put unlikely
>>> on all error handling paths.
>>> (I like unlikely for error paths specially for readability)
>>
>> "unlikely()" is not a readability hint, it's specifically for branches
>> that profiling shows adding it makes a difference.  Just delete them
>> all until profiling show they make a difference.  They certainly don't
>> make a difference in the slow paths.
>>
>
> Why?

Because the compiler and cpu already does a decent job, and if you get
the frequency wrong it can hurt performance [1].

It's pre-mature optimization to sprinkle them around, especially in slow paths.

[1]: https://lwn.net/Articles/420019/
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