From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758229AbbA3TDb (ORCPT ); Fri, 30 Jan 2015 14:03:31 -0500 Received: from mail-we0-f169.google.com ([74.125.82.169]:62235 "EHLO mail-we0-f169.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751763AbbA3TD3 (ORCPT ); Fri, 30 Jan 2015 14:03:29 -0500 From: Daniel Thompson To: Thomas Gleixner , John Stultz Cc: Daniel Thompson , linux-kernel@vger.kernel.org, patches@linaro.org, linaro-kernel@lists.linaro.org, Sumit Semwal , Stephen Boyd , Steven Rostedt Subject: [PATCH v3 0/4] sched_clock: Optimize and avoid deadlock during read from NMI Date: Fri, 30 Jan 2015 19:03:18 +0000 Message-Id: <1422644602-11953-1-git-send-email-daniel.thompson@linaro.org> X-Mailer: git-send-email 1.9.3 In-Reply-To: <1421859236-19782-1-git-send-email-daniel.thompson@linaro.org> References: <1421859236-19782-1-git-send-email-daniel.thompson@linaro.org> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org This patchset optimizes the generic sched_clock implementation to significantly reduce the data cache profile. It also makes it safe to call sched_clock() from NMI (or FIQ on ARM). The data cache profile of sched_clock() in both the original code and my previous patch was somewhere between 2 and 3 (64-byte) cache lines, depending on alignment of struct clock_data. After patching, the cache profile for the normal case should be a single cacheline. NMI safety was tested on i.MX6 with perf drowning the system in FIQs and using the perf handler to check that sched_clock() returned monotonic values. At the same time I forcefully reduced kt_wrap so that update_sched_clock() is being called at >1000Hz. Without the patches the above system is grossly unstable, surviving [9K,115K,25K] perf event cycles during three separate runs. With the patch I ran for over 9M perf event cycles before getting bored. v3: * Optimized to minimise cache profile, including elimination of the suspended flag (Thomas Gleixner). * Replaced the update_bank_begin/end with a single update function (Thomas Gleixner). * Split into multiple patches to aid review. v2: * Extended the scope of the read lock in sched_clock() so we can bank all data consumed there (John Stultz) Daniel Thompson (4): sched_clock: Match scope of read and write seqcounts sched_clock: Optimize cache line usage sched_clock: Remove suspend from clock_read_data sched_clock: Avoid deadlock during read from NMI kernel/time/sched_clock.c | 163 ++++++++++++++++++++++++++++++---------------- 1 file changed, 107 insertions(+), 56 deletions(-) -- 1.9.3