From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 87D7CC2D0EE for ; Mon, 30 Mar 2020 15:34:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 68D0A20409 for ; Mon, 30 Mar 2020 15:34:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729379AbgC3PeO convert rfc822-to-8bit (ORCPT ); Mon, 30 Mar 2020 11:34:14 -0400 Received: from eu-smtp-delivery-151.mimecast.com ([146.101.78.151]:35442 "EHLO eu-smtp-delivery-151.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728825AbgC3PeN (ORCPT ); Mon, 30 Mar 2020 11:34:13 -0400 Received: from AcuMS.aculab.com (156.67.243.126 [156.67.243.126]) (Using TLS) by relay.mimecast.com with ESMTP id uk-mta-29-3T7qKML-MqukwX-6L-zRCQ-1; Mon, 30 Mar 2020 16:34:09 +0100 X-MC-Unique: 3T7qKML-MqukwX-6L-zRCQ-1 Received: from AcuMS.Aculab.com (fd9f:af1c:a25b:0:43c:695e:880f:8750) by AcuMS.aculab.com (fd9f:af1c:a25b:0:43c:695e:880f:8750) with Microsoft SMTP Server (TLS) id 15.0.1347.2; Mon, 30 Mar 2020 16:34:08 +0100 Received: from AcuMS.Aculab.com ([fe80::43c:695e:880f:8750]) by AcuMS.aculab.com ([fe80::43c:695e:880f:8750%12]) with mapi id 15.00.1347.000; Mon, 30 Mar 2020 16:34:08 +0100 From: David Laight To: 'Steven Rostedt' CC: Linux Kernel Mailing List Subject: RE: ftrace not showing the process names for all processes on syscall events Thread-Topic: ftrace not showing the process names for all processes on syscall events Thread-Index: AdYGnj+cWqFtVCqqTmCXgoqvHM5xrf///P+A///qkvA= Date: Mon, 30 Mar 2020 15:34:08 +0000 Message-ID: <7dec110c2dc14792ba744419a4eb907e@AcuMS.aculab.com> References: <3cdef49951734e83a14959628233d4f0@AcuMS.aculab.com> <20200330110855.437fe854@gandalf.local.home> In-Reply-To: <20200330110855.437fe854@gandalf.local.home> Accept-Language: en-GB, en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-ms-exchange-transport-fromentityheader: Hosted x-originating-ip: [10.202.205.107] MIME-Version: 1.0 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: aculab.com Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Steven Rostedt > Sent: 30 March 2020 16:09 > On Mon, 30 Mar 2020 14:28:01 +0000 > David Laight wrote: > > > I've just updated one of my systems to 5.6.0-rc7+ (end of last week). > > ftrace in showing <...>-3179 in the system call events for a couple > > of threads of the active processes. > > Other threads of the same processes are fine. > > The scheduler process switch events also show the full name. > > > > Is this a known regression? > > > Well, that code hasn't changed in years. But can you explain more of what > you did? Was this the "trace" file, or "trace_pipe" file? The command names > are cached in an array (see /sys/kernel/tracing/saved_cmdlines) of the size > that is defined by the saved_cmdlines_size file. It was the 'trace' file - ie the text formatted by the kernel. I've looked at a lot of traces over the last few weeks and not seen it before. The workload is the same, so I assumed there might be a kernel change. I've just updated from a 5.4-rc7 kernel to a 5.6-rc7 one. > The cmdlines get updated via the sched_switch and sched_waking trace > events. The update is protected by a spinlock, which is only taken with a > "trylock", if the lock fails, then it does not get updated (we don't want > to hold back the running code just to cache the name of an event), but it > will try at the next sched event until it succeeds. This means that under > strong contention, it may fail to cache certain names. I've not got a silly number of context switches. But it seemed to have consistently lost some process names even when they went idle and then resumed. I would have been tracing the schedule process wakeup and switch events, system call entry/exit and irq+softirq. > This is not a regression, it's really just the work load that can cause > event names to be missed. I could work on something that if you have the > sched events enabled, that the output side could do its own caching to get > better results. Ok if nothing has changed I'll stop worrying and work out what I've broken. Oh, does the 'function_graph' code ignore tail calls? David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)