Why is stat slow?

[Eliot Moss]

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