Dear Eliot,
As a longtime aficionado of these issues, Cygwin/MSYS2 stat() function
is inherently slower than native Linux/WSL stat() syscall, because the
native stat returns data already kept and cached for each file system
inode/MFTE, while the Cygwin emulation goes through a lot of hoops to
synthesize similar information from a variety of file system data . The
call path that uses GetFileInformationByHandle() is the closest to a
native fast implementation, but unfortunately, most 21st century
antivirus solutions tend to initiate a full "scan file on open to
prevent passing infected data to vulnerable applications" cost when
doing the proforma file open to get the file handle needed for the
GetFileInformationByHandle() call or other low risk checks .
Another set of hoops in the stat() code is the synthesis of a simulated
set of mode bits, which tends to bring in the entire ACL
reinterpretation logic as well as detection of various symlink
approximations (it would be faster to simply treat all "reparse points"
as symlinks and add logic to readlink() that deals with the various
native types, but that would loose the ability to create file system
symlinks without the Administrator privilege of creating the more
dangerous system objects also named "symlink" ).
If the false triggering of AV scanning can be avoided, streamlining the
Cygwin stat() code could greatly speed up heavy users of stat() such as
the find and du commands .
On 22/12/2025 06:15, Eliot Moss via Cygwin wrote:
Dear Cygwin-ers --
I'm sure this has been asked before, more than once, but I am again
wondering
what, specifically, makes stat (the program, but presumably also the
syscall)
substantially slower on Cygwin compared to stat on WSL2. I am talking
about
an external HDD (not solid state) on my D: drive. It shows under WSL
2 as
/mnt/d like this (output of mount):
D:\ on /mnt/d type 9p
(rw,noatime,aname=drvfs;path=D:\;uid=0;gid=0;symlinkroot=/mnt/,cache=5,access=client,msize=65536,trans=fd,rfd=5,wfd=5)
On Cygwin it shows up like this (yes, mount shows two lines):
D: on /cygdrive/d type ntfs (binary,notexec,posix=0,user)
D: on /cygdrive/d type ntfs (binary,noacl,posix=0,user,noumount,auto)
My /etc/fstab lines are:
none /cygdrive cygdrive binary,noacl,posix=0,user 0 0
d: /cygdrive/d ntfs binary,posix=0,user,auto,notexec 0 0
(Presumably this has something to do with two mounts showing ...)
On D; I have a folder with hundreds of 2Gb files (they are backups,
split into
2Gb portions). On Cygwin
time stat <the files> gives
real 2m12.425s
user 0m0.249s
sys 0m1.312s
A second run shortly after the first completes very quickly,
indicating the
presence of a cache :-) .
time stat <the files> on WSL2 gives:
real 0m2.208s
user 0m0.026s
sys 0m0.149s
This is after a reboot, so there is no caching available. So, why is
Cygwin
60 times slower, even when WSL2 has the handicap of having to work
through the
9p adapter / COM surrogate?
Mostly I am curious, but this is also relevant because I rsync this file
collection to offsite storage, and the stat time is about what it
takes for
rsync to start up - it needs to check file times and lengths.
This makes me wonder if there is something we can do to make this
better, by
figuring out what WSL2 / 9p are doing ...
Best - Eliot Moss
Enjoy
Jakob
--
Jakob Bohm, CIO, Partner, WiseMo A/S. https://www.wisemo.com
Transformervej 29, 2860 Søborg, Denmark. Direct +45 31 13 16 10
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