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Re: Improving Emacs performance on Cygwin


From: Ken Brown
Subject: Re: Improving Emacs performance on Cygwin
Date: Tue, 27 Jul 2010 16:30:00 -0400
User-agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.9.2.4) Gecko/20100608 Thunderbird/3.1

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



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