On 12/22/2025 12:58 AM, Marco Atzeri via Cygwin wrote:
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
I do not notice a slow run.
The disk is an external 1T USB3 hard disk
$ time stat /dev/sdb1
File: /dev/sdb1
Size: 0 Blocks: 0 IO Block: 65536 block special file
Device: 8,17 Inode: 524305 Links: 1 Device type: 8,17
Access: (0666/brw-rw-rw-) Uid: (197608/ Marco) Gid: (197121/ NESSUNO)
Access: 2025-12-22 06:55:21.968106000 +0100
Modify: 2025-12-22 06:55:21.968106000 +0100
Change: 2025-12-22 06:55:21.968106000 +0100
Birth: 2025-12-22 06:55:21.968106000 +0100
real 0m0.099s
user 0m0.030s
sys 0m0.000s
$ time stat /cygdrive/d
File: /cygdrive/d
Size: 0 Blocks: 8 IO Block: 65536 directory
Device: 54787,64366 Inode: 1407374883553285 Links: 1
Access: (0770/drwxrwx---) Uid: ( 18/ SYSTEM) Gid: ( 18/ SYSTEM)
Access: 2025-12-21 19:40:02.793348100 +0100
Modify: 2025-11-11 15:18:10.162456400 +0100
Change: 2025-11-11 15:18:10.162456400 +0100
Birth: 2018-04-11 15:14:25.158842400 +0200
real 0m0.028s
user 0m0.015s
sys 0m0.000s
Thank you for checking, Marco! I do wonder wonder, though, if those files are
very characteristic. The first is a block file and the second is a directory.
My timings were for moderately large regular files (2Gb each), about 1300 of
them. So I guess that either there's something different about my system or
different about the files I was stat-ing.
I also wonder if anyone familiar with the internal code may have thoughts on
this ...
Best - Eliot
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