From owner-freebsd-bugs@FreeBSD.ORG Tue May 19 19:16:05 2015 Return-Path: Delivered-To: freebsd-bugs@FreeBSD.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by hub.freebsd.org (Postfix) with ESMTPS id 22E618BE for ; Tue, 19 May 2015 19:16:05 +0000 (UTC) Received: from kenobi.freebsd.org (kenobi.freebsd.org [IPv6:2001:1900:2254:206a::16:76]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by mx1.freebsd.org (Postfix) with ESMTPS id E6E9C1929 for ; Tue, 19 May 2015 19:16:04 +0000 (UTC) Received: from bugs.freebsd.org ([127.0.1.118]) by kenobi.freebsd.org (8.14.9/8.14.9) with ESMTP id t4JJG4Qu098525 for ; Tue, 19 May 2015 19:16:04 GMT (envelope-from bugzilla-noreply@freebsd.org) 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 Date: Tue, 19 May 2015 19:16:04 +0000 X-Bugzilla-Reason: AssignedTo X-Bugzilla-Type: changed X-Bugzilla-Watch-Reason: None X-Bugzilla-Product: Base System X-Bugzilla-Component: kern X-Bugzilla-Version: 11.0-CURRENT X-Bugzilla-Keywords: X-Bugzilla-Severity: Affects Only Me X-Bugzilla-Who: commit-hook@freebsd.org X-Bugzilla-Status: New X-Bugzilla-Priority: --- X-Bugzilla-Assigned-To: freebsd-bugs@FreeBSD.org X-Bugzilla-Target-Milestone: --- X-Bugzilla-Flags: X-Bugzilla-Changed-Fields: Message-ID: In-Reply-To: References: Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit X-Bugzilla-URL: https://bugs.freebsd.org/bugzilla/ Auto-Submitted: auto-generated MIME-Version: 1.0 X-BeenThere: freebsd-bugs@freebsd.org X-Mailman-Version: 2.1.20 Precedence: list List-Id: Bug reports List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 19 May 2015 19:16:05 -0000 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.