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Date: Tue, 14 Feb 2012 09:44:39 -0500
From: Ryan Johnson <ryan DOT johnson AT cs DOT utoronto DOT ca>
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To: cygwin AT cygwin DOT com
Subject: Re: File operations really slow in emacs
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On 14/02/2012 8:52 AM, Corinna Vinschen wrote:
> On Feb 14 08:37, Ryan Johnson wrote:
>> Bump?
> Stagger!
>
>> On 13/02/2012 8:31 AM, Ryan Johnson wrote:
>>> On 11/02/2012 5:11 AM, Corinna Vinschen wrote:
>>>> On Feb 10 20:18, Ryan Johnson wrote:
>>>>> Hi all,
>>>>>
>>>>> For some reason file operations have become very slow inside emacs
>>>>> starting yesterday. It's especially painful when saving a file
>>>>> that's managed by mercurial (more than 20 seconds!), but I've seen
>>>>> it on the command line as well (x-server takes a similar amount of
>>>>> time to start, for example). I'm running the latest everything and
>>>>> I've run rebaseall. I verified that Windows Defender did not
>>>>> silently re-enable itself since I last disabled it (you can't
>>>>> actually uninstall it) and no other BLODA are present on my machine.
>>>>> The problem persists across reboots.
>>>>>
>>>>> I have vague memories that this has turned up in the past (maybe
>>>>> 12-15 months ago?) but Google isn't turning up anything. Attaching
>>>>> strace to emacs during the save makes it take a full 35 seconds and
>>>>> reports the following:
>>>>>
>>>>> $ cat emacs.strace | awk '{if ($1>   1000000) { print }}' | grep -v
>>>>> timer_thread
>>>>> 26910790 26912157 [main] emacs-X11 5188 child_copy: dll bss - hp
>>>>> 0x264 low 0x611FC000, high 0x61230770, res 1
>>>>> 1128419 2125655 [main] python2.6 5188 read: read(5, 0x8009DB60,
>>>>> 65536) blocking
>>>>> 25850184 32830582 [main] python2.6 5188 stat_worker: 0 =
>>>>> (\??\C:\cygwin\cygdrive,0x28BB68)
>>>>    ^^^^^^^^^^^^^^^^^^^^^^^
>>>>    This looks suspicious.  I assume you're suffering from SMB network
>>>>    scanning.
>>> is there a workaround? Neither "always run elevated" nor "always
>>> keep all network drives mounted" seems like a reasonable
>>> requirement
> What are you expecting?  Was my reply in
> http://cygwin.com/ml/cygwin/2012-02/msg00375.html not sufficient?
The reply explains why running elevated avoids the problem -- apparently 
a side-effect of Windows' user token handling.

It does not explain why it's a good idea to always run elevated to get a 
side effect that compensates for bad behavior which is arguably a bug 
(though that's what I'm doing right now for lack of a better option -- I 
often work off-grid, so I can't always have all network drives mapped).

AFAICT, `stat /cydrive` runs into trouble because it enumerates all 
drive letters using GetFileAttributes, and only counts local drives as 
"links" to the "directory" : 2 + ndrives - nfloppies - nnonlocal. This 
relies on the fact (a side effect?) that GetFileAttributes returns 
ERROR_BAD_NETPATH for network shares (but apparently only after timing 
out an attempt to connect disconnected ones). Not sure what happens for 
USB drives (are they "floppies" ?). Is there no other way to enumerate 
the local drives, and even if there isn't, does anybody actually care 
about that particular link count? AFAIK, directory link counts only 
matter when you want to run fsck (which cygwin doesn't have) or delete a 
directory. Even if cygwin's rm pays attention to link counts, which I 
doubt, anyone issuing `rm -rf /cygdrive` has far bigger problems on 
their hands.

Ryan

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