From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757750Ab3APV4t (ORCPT ); Wed, 16 Jan 2013 16:56:49 -0500 Received: from mail.linuxfoundation.org ([140.211.169.12]:41846 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757620Ab3APV4s (ORCPT ); Wed, 16 Jan 2013 16:56:48 -0500 Date: Wed, 16 Jan 2013 13:56:47 -0800 From: Andrew Morton To: Nathan Zimmer Cc: mingo@redhat.com, peterz@infradead.org, tglx@linutronix.de, johnstul@us.ibm.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH RESEND 2/4] sched: /proc/sched_debug fails on very very large machines. Message-Id: <20130116135647.019cbe8d.akpm@linux-foundation.org> In-Reply-To: <1358286372-13777-3-git-send-email-nzimmer@sgi.com> References: <1358286372-13777-1-git-send-email-nzimmer@sgi.com> <1358286372-13777-3-git-send-email-nzimmer@sgi.com> X-Mailer: Sylpheed 3.0.2 (GTK+ 2.20.1; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 15 Jan 2013 15:46:10 -0600 Nathan Zimmer wrote: > On systems with 4096 cores attemping to read /proc/sched_debug fails. > We are trying to push all the data into a single kmalloc buffer. > The issue is on these very large machines all the data will not fit in 4mb. > > A better solution is to not us the single_open mechanism but to provide > our own seq_operations and treat each cpu as an individual record. > > The output should be identical to previous version. > > ... > > + int cpu = (unsigned long)(v - 2); Again, the meaning of the magic offsets are unobvious to readers of this code. > - SEQ_printf(m, "\n"); > + if (cpu != -1) > + print_cpu(m, cpu); Same concerns with cpu hotplug. > + else > + sched_debug_header(m); > > return 0; > }