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Subject:	Re: Cygwin a bit slow
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Date:	Wed, 10 Apr 2024 12:34:02 +0200
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From:	Christian Franke via Cygwin <cygwin AT cygwin DOT com>
Reply-To:	cygwin AT cygwin DOT com
Cc:	Christian Franke <Christian DOT Franke AT t-online DOT de>
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J M via Cygwin wrote:
> ...
>
> Specifically for this problem, I have investigated the problem and can be
> related to pipes and antivirus.
>
> Specifically
> while true
> do
> echo ABC | grep AAA
> done
>
> It makes the cpu of that antivirus go up.

This is as expected because malware scanners hook into Win32 API's 
CreateProcess*() calls which are also used by the fork()/exec() 
emulation of Cygwin. Each run of 'grep' above uses at least two 
CreateProcess*() calls.

This quick test shows how many 'date' commands could be run per second:

$ while :; do date +%s; done | uniq -c
...
      65 1712742865 <== Windows Defender off
      66 1712742866
      66 1712742867
      64 1712742868
      61 1712742869
      51 1712742870 <== Windows Defender turned on
      51 1712742871
      49 1712742872
      45 1712742873
      53 1712742874
      54 1712742875
...

The above could even slow down to 1-2 per second with certain malware 
scanners if expensive heuristics (which may also generate a lot of false 
positives, BTW) is enabled. So one problem is the lousy performance of 
CreateProcess*() calls. This is not Cygwin-specific but affects typical 
Cygwin use cases like shell scripts.

Using bash builtins in the above example speeds it up to ~21000/second 
on the same very old box:

$ while :; do printf '%(%s)T\n'; done | uniq -c

-- 
Regards,
Christian


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