From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751404Ab2DUE1n (ORCPT ); Sat, 21 Apr 2012 00:27:43 -0400 Received: from hrndva-omtalb.mail.rr.com ([71.74.56.122]:2474 "EHLO hrndva-omtalb.mail.rr.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750800Ab2DUE1m (ORCPT ); Sat, 21 Apr 2012 00:27:42 -0400 X-Authority-Analysis: v=2.0 cv=V/z/IJbi c=1 sm=0 a=ZycB6UtQUfgMyuk2+PxD7w==:17 a=XQbtiDEiEegA:10 a=lt3JZn9S7PoA:10 a=5SG0PmZfjMsA:10 a=Q9fys5e9bTEA:10 a=IFFSxcZ83qxRnnNlgCYA:9 a=B3yhWHvGVk21BXoNxLgA:7 a=PUjeQqilurYA:10 a=ZycB6UtQUfgMyuk2+PxD7w==:117 X-Cloudmark-Score: 0 X-Originating-IP: 74.67.80.29 Message-ID: <1334982460.28106.90.camel@gandalf.stny.rr.com> Subject: Re: [PATCH v5 2/4] trace: Make removal of ring buffer pages atomic From: Steven Rostedt To: Vaibhav Nagarnaik Cc: Frederic Weisbecker , Ingo Molnar , Michael Rubin , David Sharp , Justin Teravest , linux-kernel@vger.kernel.org Date: Sat, 21 Apr 2012 00:27:40 -0400 In-Reply-To: <1328212844-11889-2-git-send-email-vnagarnaik@google.com> References: <1318382410-14967-1-git-send-email-vnagarnaik@google.com> <1328212844-11889-1-git-send-email-vnagarnaik@google.com> <1328212844-11889-2-git-send-email-vnagarnaik@google.com> Content-Type: text/plain; charset="ISO-8859-15" X-Mailer: Evolution 3.2.2-1 Content-Transfer-Encoding: 7bit Mime-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 2012-02-02 at 12:00 -0800, Vaibhav Nagarnaik wrote: > This patch adds the capability to remove pages from a ring buffer > without destroying any existing data in it. > > This is done by removing the pages after the tail page. This makes sure > that first all the empty pages in the ring buffer are removed. If the > head page is one in the list of pages to be removed, then the page after > the removed ones is made the head page. This removes the oldest data > from the ring buffer and keeps the latest data around to be read. > > To do this in a non-racey manner, tracing is stopped for a very short > time while the pages to be removed are identified and unlinked from the > ring buffer. The pages are freed after the tracing is restarted to > minimize the time needed to stop tracing. > > The context in which the pages from the per-cpu ring buffer are removed > runs on the respective CPU. This minimizes the events not traced to only > NMI trace contexts. Can't do this. (see below) > +rb_remove_pages(struct ring_buffer_per_cpu *cpu_buffer, unsigned int > nr_pages) > { > - struct buffer_page *bpage; > - struct list_head *p; > - unsigned i; > + unsigned int nr_removed; > + int page_entries; > + struct list_head *tail_page, *to_remove, *next_page; > + unsigned long head_bit; > + struct buffer_page *last_page, *first_page; > + struct buffer_page *to_remove_page, *tmp_iter_page; > Also, please use the "upside down x-mas tree" for the declarations: ie. struct list_head *tail_page, *to_remove, *next_page; struct buffer_page *to_remove_page, *tmp_iter_page; struct buffer_page *last_page, *first_page; unsigned int nr_removed; unsigned long head_bit; int page_entries; See, it looks easier to read then what you had. > + /* fire off all the required work handlers */ > + for_each_buffer_cpu(buffer, cpu) { > + cpu_buffer = buffer->buffers[cpu]; > + if (!cpu_buffer->nr_pages_to_update) > + continue; > + schedule_work_on(cpu, &cpu_buffer->update_pages_work); This locks up. I just tried the following, and it hung the task. Here: # cd /sys/kernel/debug/tracing # echo 1 > events/enable # sleep 10 # echo 0 > event/enable # echo 0 > /sys/devices/system/cpu/cpu1/online # echo 100 > buffer_size_kb I guess you could test if the cpu is online. And if so, then do the schedule_work_on(). You will need to get_online_cpus first. If the cpu is offline, just change it. -- Steve PS. The first patch looks good, but I think you need to add some more blank lines in your patches. You like to bunch a lot of text together, and that causes some eye strain.