From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760464AbbCDIfy (ORCPT ); Wed, 4 Mar 2015 03:35:54 -0500 Received: from e7.ny.us.ibm.com ([32.97.182.137]:54927 "EHLO e7.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1760446AbbCDIfw (ORCPT ); Wed, 4 Mar 2015 03:35:52 -0500 From: Sukadev Bhattiprolu To: Michael Ellerman , Paul Mackerras , peterz@infradead.org Cc: dev@codyps.com, , linuxppc-dev@lists.ozlabs.org Subject: [PATCH 0/4] perf: Implement event group read using txn interface Date: Wed, 4 Mar 2015 00:35:04 -0800 Message-Id: <1425458108-3341-1-git-send-email-sukadev@linux.vnet.ibm.com> X-Mailer: git-send-email 1.7.9.5 X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 15030408-0037-0000-0000-000000C60352 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Unlike normal hardware PMCs, the 24x7 counters[1] in Power8 are stored in memory and accessed via a hypervisor call (HCALL). A major aspect of the HCALL is that it allows retireving _SEVERAL_ counters at once (unlike regular PMCs, which are read one at a time). By reading several counters at once, we can get a more consistent snapshot of the system. This patchset explores the possibility of using the transaction interface to accomplish submitting several "events" to the PMU and have the PMU read them all at once. User is expected to submit the set of events they want to read as an "event group". In the kernel, we submit each event to the PMU using the following logic (from Peter Zijlstra). pmu->start_txn(pmu, PMU_TXN_READ); leader->read(); for_each_sibling() sibling->read(); pmu->commit_txn(); where: - the ->read()s queue events to be submitted to the hypervisor, and, - the ->commit_txn() issues the HCALL, retrieves the result and updates the event count. Since the ->commit_txn() updates the event count, perf subsystem can use the event count directly and skip the a ->read() call immediately after the transaction. TODO: - Lightly tested on Powerpc; Needs more testing on Power and x86. - Need to review/update txn and perf_event_read_value() interfaces for other architectures. Thanks to Peter Zijlstra for his input. Sukadev Bhattiprolu (4): perf: Add 'flags' parameter to pmu txn interfaces perf: Split perf_event_read() and perf_event_count() perf: Add 'update' parameter to perf_event_read_value() perf/powerpc: Implement group_read() txn interface for 24x7 counters arch/powerpc/perf/core-book3s.c | 15 +++- arch/powerpc/perf/hv-24x7.c | 171 +++++++++++++++++++++++++++++++++++++++ arch/x86/kernel/cpu/perf_event.c | 15 +++- arch/x86/kvm/pmu.c | 2 +- include/linux/perf_event.h | 17 +++- kernel/events/core.c | 93 ++++++++++++++++----- 6 files changed, 281 insertions(+), 32 deletions(-) -- 1.8.3.1