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Subject: Re: long I/O delays when strace is running
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References: <be8713ec-5b68-e0e9-c5a5-d48fce491a2d@pobox.com> <91DCAC3CB99C724EB365BB64677FBE7B16EBBD@MX204CL04.corp.emc.com> <46e39bce-9782-5c74-c196-35ee97ebbc64@pobox.com> <ace81c86-80d5-bef9-6b93-7d36dde5a4e8@pobox.com>
From: Daniel Santos <daniel.santos@pobox.com>
Message-ID: <bff9c5ea-85d9-bf4e-2f25-271c1490565f@pobox.com>
Date: Fri, 21 Apr 2017 00:44:24 -0500
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I've tracked it down to this little Sleep() loop in pinfo::init.

       bool created = shloc != SH_JUSTOPEN;

       /* Detect situation where a transitional memory block is being 
retrieved.
      If the block has been allocated with PINFO_REDIR_SIZE but not yet
      updated with a PID_EXECED state then we'll retry. */
       if (!created && !(flag & PID_NEW))
     /* If not populated, wait 2 seconds for procinfo to become populated.
        Would like to wait with finer granularity but that is not easily
        doable.  */
     for (int i = 0; i < 200 && !procinfo->ppid; i++)
       Sleep (10);

I tried putting a stupid memory barrier in the loop and a volatile read 
just for kicks, but that doesn't seem to be the problem.  I'm headed off 
to bed.  This only happens when using strace, so if anybody has ideas 
please post.

Daniel

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