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Message-ID:	<002301c0756a$2ed35980$0200a8c0@lifelesswks>
From:	"Robert Collins" <robert DOT collins AT itdomain DOT com DOT au>
To:	"Dan Morris" <dmorris AT tiqit DOT com>, <cygwin AT sources DOT redhat DOT com>
References:	<Pine DOT GSO DOT 4 DOT 21 DOT 0101030036510 DOT 14474-100000 AT fable6 DOT Stanford DOT EDU>
Subject:	Re: Cygwin fstat and NT caching
Date:	Wed, 3 Jan 2001 20:47:24 +1100
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IIRC stat() on cygwin reads the files magic number to see if it is executable (in addition to using the exec permissions when ntsec
is on).




----- Original Message -----
From: "Dan Morris" <dmorris AT tiqit DOT com>
To: <cygwin AT sources DOT redhat DOT com>
Sent: Wednesday, January 03, 2001 7:52 PM
Subject: Cygwin fstat and NT caching


> My supervisor pointed out to me yesterday that "du" takes a long time to run
> under Cygwin; out of curiosity, I've been looking into the source of the
> delays, and I'm curious if anyone else has any insights...
>
> This is me running 'du' on my entire hard drive under cygwin :
>
> dmorris AT SOAPY /edrive
> $ time du
>
> ... blah blah blah ... all my files go by ... disk spins like mad ...
>
> ... I get some coffee ...
>
> 0       ./cygwin/edrive
> 1       ./cygwin/.ssh
> 208758  ./cygwin
> 7336071 .
>
> real    5m35.523s
> user    0m10.064s
> sys     0m32.877s
>
> Five minutes is a long time.
>
> Now this is me running the Windy Tree CommandPack's version of "du" on the
> same drive, from inside Cygwin (so I can use "time") :
>
> dmorris AT SOAPY /edrive
> $ time /edrive/Program\ Files/utils/commands/du.exe
>
> Windy Tree CommandPack - du (diskusage)
> (C) Copyright 1999 by Windy Tree. More info at www.windytree.com
> -------------------------------------------------------------------------------
>
> ... files race by quickly ... disk doesn't move ... clearly using cached
> inodes...
>
>    4775838      e:\cygwin\home
>          0      e:\cygwin\edrive
>        350      e:\cygwin\.ssh
>  209518621      e:\cygwin
>
> 7494592864 Bytes total in 67845 files, 4516 directories
>
> real    0m35.301s
> user    0m0.170s
> sys     0m0.120s
>
>
> Thirty seconds for WindyTree, five minutes for Cygwin; this result is
> repeatable (that is, the result you see above doesn't mean that I'm just
> running the Cygwin version first, then letting the WindyTree version take
> advantage of all the caching).
>
> Anyone know why this might be?  I looked through the du code; the only
> repeated filesystem access seems to be through stat() and lstat().  So I
> looked through stat() and lstat(), and I can't see any place where disk
> flushes are explicitly forced, or any place where Win32 calls are made with
> specific flags for ignoring the inode cache ... these seem to be the Win32
> filesystem calls that get made :
>
> GetVolumeInformation
> GetDriveType
> GetFileInformationByHandle
> GetFileSize
> GetFileType
> FindFirstFile
>
> I don't know why any of them would ignore the cache... any ideas?  I'm
> running Win2000, if that helps anyone...
>
> Thanks...
>
> -Dan
>
> Dan Morris
> http://techhouse.brown.edu/dmorris
>
> Tiqit Computers
> http://www.tiqit.com
>
>
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>
>


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