[newlib-cygwin/main] Cygwin: faq: add test of fork/exec slowdown by anti-virus

[Christian Franke]

https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;h=ac28fce85cc4d8f85c2cf10bb52d39f33ec38ed6

commit ac28fce85cc4d8f85c2cf10bb52d39f33ec38ed6
Author: Christian Franke <christian.franke@t-online.de>
Date:   Sat Mar 29 16:34:33 2025 +0100

    Cygwin: faq: add test of fork/exec slowdown by anti-virus
    
    Signed-off-by: Christian Franke <christian.franke@t-online.de>

Diff:
---
 winsup/doc/faq-using.xml | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/winsup/doc/faq-using.xml b/winsup/doc/faq-using.xml
index 4dc462a0a..e5e4479f5 100644
--- a/winsup/doc/faq-using.xml
+++ b/winsup/doc/faq-using.xml
@@ -956,6 +956,26 @@ contents are exempt from scanning.  In a default installation, this
 would be <literal>C:\cygwin\bin</literal>.  Obviously, this could be
 exploited by a hostile non-Cygwin program, so do this at your own risk.
 </para>
+<para>Anti-virus software typically reduce the speed of Windows
+<literal>CreateProcess</literal> calls which are used by Cygwin to provide
+<literal>fork()</literal> and <literal>exec()</literal>.  This in particular
+slows down shell scripts.  In the simple speed test shown below, the first
+column shows the number of <literal>date</literal> commands run per second.
+Anti-virus was turned off at the line marked with <literal>***</literal>.
+</para>
+<screen>
+	bash$ while :; do date +%s; done | uniq -c
+	...
+	122 1741712430
+	118 1741712431
+	118 1741712432
+	121 1741712433
+	142 1741712434  ***
+	140 1741712435
+	141 1741712436
+	144 1741712437
+	...
+</screen>
 <para>See also <xref linkend="faq.using.bloda"></xref>
 for a list of applications that have been known, at one time or another, to
 interfere with the normal functioning of Cygwin.