From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753354AbcFTHus (ORCPT ); Mon, 20 Jun 2016 03:50:48 -0400 Received: from LGEAMRELO11.lge.com ([156.147.23.51]:46097 "EHLO lgeamrelo11.lge.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753307AbcFTHuk convert rfc822-to-8bit (ORCPT ); Mon, 20 Jun 2016 03:50:40 -0400 X-Original-SENDERIP: 156.147.1.127 X-Original-MAILFROM: byungchul.park@lge.com X-Original-SENDERIP: 10.177.220.139 X-Original-MAILFROM: byungchul.park@lge.com From: "byungchul.park" To: "'xinhui'" , , Cc: , , , , References: <1466398527-1122-1-git-send-email-byungchul.park@lge.com> <1466398527-1122-13-git-send-email-byungchul.park@lge.com> <57679B57.40905@linux.vnet.ibm.com> In-Reply-To: <57679B57.40905@linux.vnet.ibm.com> Subject: RE: [RFC 12/12] x86/dumpstack: Optimize save_stack_trace Date: Mon, 20 Jun 2016 16:50:37 +0900 Message-ID: <000101d1cac8$6f321c40$4d9654c0$@lge.com> MIME-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8BIT X-Mailer: Microsoft Outlook 14.0 Thread-Index: AQFdImE/HMhe2H9+VitPid1gmvlQiQGp+YBSAeHofq2gvuvxgA== Content-Language: ko Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > -----Original Message----- > From: xinhui [mailto:xinhui.pan@linux.vnet.ibm.com] > Sent: Monday, June 20, 2016 4:29 PM > To: Byungchul Park; peterz@infradead.org; mingo@kernel.org > Cc: linux-kernel@vger.kernel.org; npiggin@suse.de; walken@google.com; > ak@suse.de; tglx@inhelltoy.tec.linutronix.de > Subject: Re: [RFC 12/12] x86/dumpstack: Optimize save_stack_trace > > > On 2016年06月20日 12:55, Byungchul Park wrote: > > Currently, x86 implementation of save_stack_trace() is walking all stack > > region word by word regardless of what the trace->max_entries is. > > However, it's unnecessary to walk after already fulfilling caller's > > requirement, say, if trace->nr_entries >= trace->max_entries is true. > > > > For example, CONFIG_LOCKDEP_CROSSRELEASE implementation calls > > save_stack_trace() with max_entries = 5 frequently. I measured its > > overhead and printed its difference of sched_clock() with my QEMU x86 > > machine. > > > > The latency was improved over 70% when trace->max_entries = 5. > > > [snip] > > > +static int save_stack_end(void *data) > > +{ > > + struct stack_trace *trace = data; > > + return trace->nr_entries >= trace->max_entries; > > +} > > + > > static const struct stacktrace_ops save_stack_ops = { > > .stack = save_stack_stack, > > .address = save_stack_address, > then why not check the return value of ->address(), -1 indicate there is > no room to store any pointer. Hello, Indeed. It also looks good to me even though it has to propagate the condition between callback functions. I will modify it if it's better. Thank you. Byungchul > > > .walk_stack = print_context_stack, > > + .end_walk = save_stack_end, > > }; > > > > static const struct stacktrace_ops save_stack_ops_nosched = { > >