Re: Improving Emacs performance on Cygwin

[Ken Brown <kbrown@cornell.edu>]

On 7/27/2010 4:01 PM, Davis Herring wrote:
>> I would like to apply the following patch, which seems to give a
>> substantial performance improvement on Cygwin (and obviously has no
>> effect on other platforms).
>> [...]
>>    #define DIRENTRY_NONEMPTY(p) ((p)->d_name[0] != 0)
>>    #else
>>    #define DIRENTRY_NONEMPTY(p) ((p)->d_ino)
>
> How can looking up d_name[0] be any slower than looking up d_ino?  They're
> both already in memory (d_name is an array, not a pointer, even); are we
> really seeing a "substantial performance improvement" from a cache effect
> or something?

I don't know.

> This is a question born of curiosity, not a criticism; so long as the
> relevant version of Cygwin is properly handled (as addressed elsewhere in
> the thread) simplifying the conditional is already a win.

My initial motivation was just to simplify the code and get rid of an 
unnecessary special case for Cygwin.  I then thought I observed a 
performance improvement, but I could be wrong.  I didn't make any 
measurements.

Ken