Skip site navigation (1)Skip section navigation (2)
Date:      Tue, 19 May 2015 19:16:04 +0000
From:      bugzilla-noreply@freebsd.org
To:        freebsd-bugs@FreeBSD.org
Subject:   [Bug 198149] [hwpmc] pmcstat -P -t (top mode, process sampling) stops after a while
Message-ID:  <bug-198149-8-bqx13liq2B@https.bugs.freebsd.org/bugzilla/>
In-Reply-To: <bug-198149-8@https.bugs.freebsd.org/bugzilla/>
References:  <bug-198149-8@https.bugs.freebsd.org/bugzilla/>

next in thread | previous in thread | raw e-mail | index | archive | help
https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=198149

--- Comment #16 from commit-hook@freebsd.org ---
A commit references this bug:

Author: jhb
Date: Tue May 19 19:15:20 UTC 2015
New revision: 283123
URL: https://svnweb.freebsd.org/changeset/base/283123

Log:
  Fix two bugs that could result in PMC sampling effectively stopping.
  In both cases, the the effect of the bug was that a very small positive
  number was written to the counter. This means that a large number of
  events needed to occur before the next sampling interrupt would trigger.
  Even with very frequently occurring events like clock cycles wrapping all
  the way around could take a long time. Both bugs occurred when updating
  the saved reload count for an outgoing thread on a context switch.

  First, the counter-independent code compares the current reload count
  against the count set when the thread switched in and generates a delta
  to apply to the saved count. If this delta causes the reload counter
  to go negative, it would add a full reload interval to wrap it around to
  a positive value. The fix is to add the full reload interval if the
  resulting counter is zero.

  Second, occasionally the raw counter value read during a context switch
  has actually wrapped, but an interrupt has not yet triggered. In this
  case the existing logic would return a very large reload count (e.g.
  2^48 - 2 if the counter had overflowed by a count of 2). This was seen
  both for fixed-function and programmable counters on an E5-2643.
  Workaround this case by returning a reload count of zero.

  PR:        198149
  Differential Revision:    https://reviews.freebsd.org/D2557
  Reviewed by:    emaste
  MFC after:    1 week
  Sponsored by:    Norse Corp, Inc.

Changes:
  head/sys/dev/hwpmc/hwpmc_core.c
  head/sys/dev/hwpmc/hwpmc_mod.c

-- 
You are receiving this mail because:
You are the assignee for the bug.



Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?bug-198149-8-bqx13liq2B>