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=-7.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,SPF_PASS,USER_AGENT_MUTT autolearn=ham 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 69413C43381 for ; Tue, 26 Feb 2019 15:30:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 38AE320C01 for ; Tue, 26 Feb 2019 15:30:45 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727314AbfBZPao (ORCPT ); Tue, 26 Feb 2019 10:30:44 -0500 Received: from mx1.redhat.com ([209.132.183.28]:34534 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726539AbfBZPan (ORCPT ); Tue, 26 Feb 2019 10:30:43 -0500 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 2C86930BC753; Tue, 26 Feb 2019 15:30:43 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.43.17.31]) by smtp.corp.redhat.com (Postfix) with SMTP id D9EBD60BFB; Tue, 26 Feb 2019 15:30:41 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Tue, 26 Feb 2019 16:30:42 +0100 (CET) Date: Tue, 26 Feb 2019 16:30:40 +0100 From: Oleg Nesterov To: Jiri Slaby Cc: Andrei Vagin , Andrew Morton , linux-kernel@vger.kernel.org, "Eric W. Biederman" Subject: Re: [PATCH v2] kernel: release ptraced tasks before zap_pid_ns_processes Message-ID: <20190226153039.GA21443@redhat.com> References: <20190110175200.12442-1-avagin@gmail.com> <9049595f-5c48-6866-2769-96be697f9493@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <9049595f-5c48-6866-2769-96be697f9493@suse.cz> User-Agent: Mutt/1.5.24 (2015-08-30) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.43]); Tue, 26 Feb 2019 15:30:43 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 02/26, Jiri Slaby wrote: > > On 10. 01. 19, 18:52, Andrei Vagin wrote: > > --- a/kernel/exit.c > > +++ b/kernel/exit.c > > @@ -558,12 +558,14 @@ static struct task_struct *find_alive_thread(struct task_struct *p) > > return NULL; > > } > > > > -static struct task_struct *find_child_reaper(struct task_struct *father) > > +static struct task_struct *find_child_reaper(struct task_struct *father, > > + struct list_head *dead) > > __releases(&tasklist_lock) > > __acquires(&tasklist_lock) > > { > > struct pid_namespace *pid_ns = task_active_pid_ns(father); > > struct task_struct *reaper = pid_ns->child_reaper; > > + struct task_struct *p, *n; > > > > if (likely(reaper != father)) > > return reaper; > > @@ -579,6 +581,12 @@ static struct task_struct *find_child_reaper(struct task_struct *father) > > panic("Attempted to kill init! exitcode=0x%08x\n", > > father->signal->group_exit_code ?: father->exit_code); > > } > > + > > + list_for_each_entry_safe(p, n, dead, ptrace_entry) { > > + list_del_init(&p->ptrace_entry); > > + release_task(p); > > + } > > + > > Hi, > > from our (SUSE) QA we received a report that this patch causes a > performance decline in libmicro pthread_* benchmark as reported in: > https://bugzilla.suse.com/show_bug.cgi?id=1126762 Access Denied > I tried myself from the repo: > https://github.com/redhat-performance/libMicro > > I ran > pthread_create -B 8 -C 200 -S > > and with the patch applied: > # STATISTICS usecs/call (raw) usecs/call (outliers removed) > # mean 23.38611 17.29311 > > Without: > # mean 41.36539 39.21347 can't reproduce, I see the same numbers with or without this patch. However, I did "./bin/pthread_create -B 8 -C 200 -S" under KVM. > The benchmark seems to create 8 (-B above) pthreads, does lock/unlock in > them and then the threads exit. The benchmark reaps the threads via > pthread_join. This all happens 200 times (-C above). Given that this test-case doesn't use CLONE_PID, I fail to understand how this patch can make any noticeable difference performance wise... with this patch forget_original_parent() just passes the additional argument to find_child_reaper(), nothing else. The extra list_for_each_entry_safe/release_task loop can't happen, and even if it could it shouldn't cause any performance regression too. > Any idea how to restore the performance close to the previous state? maybe you can try perf to find out where does this difference come from? Oleg.