Re: [RFC/PATCH v2 1/1] cygwin: Add fast_lstat() and fast_fstat() functions

[Ramsay Jones <ramsay@ramsay1.demon.co.uk>]

Mark Levedahl wrote:
> On 07/10/2013 04:23 PM, Ramsay Jones wrote:
>> Commit adbc0b6b ("cygwin: Use native Win32 API for stat", 30-09-2008)
>> added a Win32 specific implementation of the stat functions. In order
>> to handle absolute paths, cygwin mount points and symbolic links, this
>> implementation may fall back on the standard cygwin l/stat() functions.
>> Also, the choice of cygwin or Win32 functions is made lazily (by the
>> first call(s) to l/stat) based on the state of some config variables.
>>
>> Unfortunately, this "schizophrenic stat" implementation has been the
>> source of many problems ever since. For example, see commits 7faee6b8,
>> 79748439, 452993c2, 085479e7, b8a97333, 924aaf3e, 05bab3ea and 0117c2f0.
>>
>> In order to limit the adverse effects caused by this implementation,
>> we provide a new "fast stat" interface, which allows us to use this
>> only for interactions with the index (i.e. the cached stat data).
>>
>> Signed-off-by: Ramsay Jones <ramsay@ramsay1.demon.co.uk>
>> ---
> 
> I've tested this on Cygwin 1.7 on WIndows 7 , comparing to the results 
> using your prior patch (removing the Cygwin specific lstat entirely) and 
> get the same results with both, so this seems ok from me.

Thank you for testing this.

> My comparison point was created by reverting your current patch from pu, 
> then reapplying your earlier patch on top, so the only difference was 
> which approach was used to address the stat functions.
> 
> Caveats:
> 1) I don't find any speed improvement of the current patch over the 
> previous one (the tests actually ran faster with the earlier patch, 
> though the difference was less than 1%).
> 2) I still question this whole approach, especially having this 
> non-POSIX compliant mode be the default. Running in this mode breaks 
> interoperability with Linux, but providing a Linux environment is the 
> *primary* goal of Cygwin.

Yes, I agree. Since I _always_ disable the Win32 stat functions (by
setting core.filemode by hand - yes it's a little annoying), I don't
get any "benefit" from the added complexity.

However, I don't use git on cygwin with *large* repositories. git.git
is pretty much as large as it gets. So, the difference in performance
for me amounts to something like 0.120s -> 0.260s, which I can barely
notice.

Other people may not be so lucky ...

I would be happy if my original patch (removing the win32 stat funcs)
was applied, but others may not be. :-P

ATB,
Ramsay Jones