Why is stat slow?

[Eliot Moss]

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