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From: "fche at redhat dot com" <sourceware-bugzilla@sourceware.org>
To: systemtap@sourceware.org
Subject: [Bug runtime/28449] New: loss of cross-cpu output ordering
Date: Wed, 13 Oct 2021 17:20:32 +0000
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https://sourceware.org/bugzilla/show_bug.cgi?id=3D28449

            Bug ID: 28449
           Summary: loss of cross-cpu output ordering
           Product: systemtap
           Version: unspecified
            Status: NEW
          Severity: normal
          Priority: P2
         Component: runtime
          Assignee: systemtap at sourceware dot org
          Reporter: fche at redhat dot com
  Target Milestone: ---

Since making bulk-mode the default back in commit 8819e2a04596d, we lost a
property of total ordering for the normal output stream (across CPUs).=20
Userspace cannot reorder messages from the individual trace$n buffers, beca=
use
the runtime no longer sends the _stp_trace->sequence number to userspace.=20
(This breaks stp_merge but whatever, it's probably not used and we could
deprecate it.)

We should bring the _stp_trace .sequence bit back (snippets of the
!NO_PERCPU_HEADERS branch), and have stapio threads synchronize lightly for
sorting on the output side.

--=20
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