From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932936AbeBLWWn (ORCPT ); Mon, 12 Feb 2018 17:22:43 -0500 Received: from smtp.codeaurora.org ([198.145.29.96]:55442 "EHLO smtp.codeaurora.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932628AbeBLWWk (ORCPT ); Mon, 12 Feb 2018 17:22:40 -0500 DMARC-Filter: OpenDMARC Filter v1.3.2 smtp.codeaurora.org A5B2160F6C Authentication-Results: pdx-caf-mail.web.codeaurora.org; dmarc=none (p=none dis=none) header.from=codeaurora.org Authentication-Results: pdx-caf-mail.web.codeaurora.org; spf=none smtp.mailfrom=rananta@codeaurora.org From: Raghavendra Rao Ananta Subject: Re: [PATCH] perf: Add support for creating offline events To: Jiri Olsa Cc: peterz@infradead.org, mingo@redhat.com, acme@kernel.org, alexander.shishkin@linux.intel.com, namhyung@kernel.org, linux-kernel@vger.kernel.org, psodagud@codeaurora.org, tsoni@codeaurora.org References: <1518217620-28458-1-git-send-email-rananta@codeaurora.org> <20180212094357.GD5821@krava> <53408020-8638-4947-90f6-87dbc4c2c4e5@codeaurora.org> <20180212210442.GA32093@krava> <20180212212101.GA15817@krava> Message-ID: <6aab2b36-0fe6-7a3d-2106-d4c93ec95a8a@codeaurora.org> Date: Mon, 12 Feb 2018 14:22:30 -0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.4.0 MIME-Version: 1.0 In-Reply-To: <20180212212101.GA15817@krava> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 02/12/2018 01:21 PM, Jiri Olsa wrote: > On Mon, Feb 12, 2018 at 10:04:42PM +0100, Jiri Olsa wrote: >> On Mon, Feb 12, 2018 at 09:42:05AM -0800, Raghavendra Rao Ananta wrote: >>> Hi Jiri, >>> >>> Thank you for the response. >>> >>> Does perf tool has its own check to see if the CPU was offline during the >>> lifetime of an event? If so, it might ignore these type of events. >> >> nope, we don't check on that >> >>> >>> Initially, I tested the same using perf tool and found similar results. >>> Then I debugged further and found that the perf core was actually sending >>> data to the userspace (copy_to_user()) and the corresponding count for the >>> data. Hence, I tested this further by writing my own userspace application, >>> and I was able to read the count through this, >>> even when the CPU was made offline and back online. >>> >>> Do you think we also have to modify the perf tool accordingly? >> >> hum, I wonder what's wrong.. will check > > I think the user space needs to enable the event once the > cpu gets online.. which we dont do and your app does..? > > maybe we could add perf_event_attr::enable_on_online ;-) > > I'll check what we can do in user space, I guess we can > monitor the cpu state and enable event accordingly > > jirka > Yes, probably that's the reason. In order for an event to get scheduled-in, it expects the event to be at least in PERF_EVENT_STATE_INACTIVE state. If you notice, in my patch, when the cpu wakes up, we are initializing the state of the event (perf_event__state_init()) and then trying to schedule-in. Since the event was created with a disabled state, it seems that the same this is followed and the state gets initialized to PERF_EVENT_STATE_OFF. Unfortunately, events in this state could not be scheduled. One way for things to get working is, instead of calling perf_event__state_init() before the event is scheduled-in (when the cpu wakes up), we can do something like: perf_event_set_state(event, PERF_EVENT_STATE_INACTIVE); I made this change and ran the same test as yours, and I see things working out for us: # ./perf stat -C 1 -e sched:sched_switch -v -I 1000 failed to read counter sched:sched_switch # time counts unit events 1.000115547 sched:sched_switch failed to read counter sched:sched_switch 2.000265492 sched:sched_switch failed to read counter sched:sched_switch 3.000379462 sched:sched_switch failed to read counter sched:sched_switch 4.000523872 sched:sched_switch failed to read counter sched:sched_switch 5.000614808 sched:sched_switch /* CPU bought ONLINE here */ sched:sched_switch: 541 284808940 284808940 6.000767761 541 sched:sched_switch sched:sched_switch: 180 1000119686 1000119686 7.000907234 180 sched:sched_switch sched:sched_switch: 248 1000129929 1000129929 8.001026518 248 sched:sched_switch sched:sched_switch: 253 1000173050 1000173050 9.001203689 253 sched:sched_switch sched:sched_switch: 620 1000113378 1000113378 10.001323334 620 sched:sched_switch sched:sched_switch: 366 1000121839 1000121839 11.001448354 366 sched:sched_switch sched:sched_switch: 327 1000147664 1000147664 12.001591432 327 sched:sched_switch ^Csched:sched_switch: 272 488810681 488810681 12.490414290 272 sched:sched_switch sched:sched_switch: 6 75893 75893 Yes, so as you mentioned adding something like perf_event_attr::enable_on_online gives us a control as to put the event in INACTIVE state. -- Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project