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To: cygwin AT cygwin DOT com
From: Daniel Santos <daniel DOT santos AT pobox DOT com>
Subject: long I/O delays when strace is running
Message-ID: <be8713ec-5b68-e0e9-c5a5-d48fce491a2d@pobox.com>
Date: Wed, 19 Apr 2017 18:05:46 -0500
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Well I've solved one problem, but now I have another one. To try to 
understand why except is getting broken pipes (child processes are 
"going away"), I modified DejaGNU's /usr/bin/runtest so that it would 
strace each except process:

-exec "$expectbin" $debug -- "$runpath"/runtest.exp $target ${1+"$@"}
+exec strace --output=/tmp/runtest.$$.log --trace-children 
--mask=startup  $expectbin $debug -- $runpath/runtest.exp $target ${1+"$@"}

However, when I run make -kj8 check after this, Cygwin processes that do 
file I/O and even ps become very unresponsive and CPU utilization is low 
(not to say that DejaGNU is good at balancing the test load). If I hit 
ctrl-C on the make process, it won't exit for somewhere around 30 
seconds.  I am able to reproduce this to some degree with this simple 
snippet, although the delays aren't as long as doing the above:

for ((i = 0; i < 64; ++i)); do strace --output=/tmp/sleep.$$.log 
--trace-children --mask=startup sleep 64; done

Can anybody try this and see if they get delays when running ps -ef or 
some such?

Thanks,
Daniel

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