Date: Mon, 01 Jun 2015 18:09:23 +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-rWjBzO2vJC@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/>
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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=198149 --- Comment #17 from commit-hook@freebsd.org --- A commit references this bug: Author: jhb Date: Mon Jun 1 18:08:58 UTC 2015 New revision: 283886 URL: https://svnweb.freebsd.org/changeset/base/283886 Log: MFC 283123: 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 Sponsored by: Norse Corp, Inc. Changes: _U stable/10/ stable/10/sys/dev/hwpmc/hwpmc_core.c stable/10/sys/dev/hwpmc/hwpmc_mod.c _U stable/9/sys/ _U stable/9/sys/dev/ stable/9/sys/dev/hwpmc/hwpmc_core.c stable/9/sys/dev/hwpmc/hwpmc_mod.c -- You are receiving this mail because: You are the assignee for the bug.
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