From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756590AbZDPBNA (ORCPT ); Wed, 15 Apr 2009 21:13:00 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754152AbZDPBMj (ORCPT ); Wed, 15 Apr 2009 21:12:39 -0400 Received: from cn.fujitsu.com ([222.73.24.84]:65086 "EHLO song.cn.fujitsu.com" rhost-flags-OK-FAIL-OK-OK) by vger.kernel.org with ESMTP id S1753908AbZDPBMi (ORCPT ); Wed, 15 Apr 2009 21:12:38 -0400 Message-ID: <49E68635.8050404@cn.fujitsu.com> Date: Thu, 16 Apr 2009 09:13:25 +0800 From: Li Zefan User-Agent: Thunderbird 2.0.0.9 (X11/20071115) MIME-Version: 1.0 To: Frederic Weisbecker CC: Ingo Molnar , Steven Rostedt , Zhaolei , Tom Zanussi , KOSAKI Motohiro , LKML , Peter Zijlstra Subject: Re: [RFC][PATCH 1/2] tracing/events: provide string with undefined size support References: <1239838050-8567-1-git-send-email-fweisbec@gmail.com> In-Reply-To: <1239838050-8567-1-git-send-email-fweisbec@gmail.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Frederic Weisbecker wrote: > Impact: less memory usage for tracing > > This patch provides the support for dynamic size strings on > event tracing. > blktrace TRACE_EVENTs need this too. :) > The key concept is to use a structure with an ending char array field of > undefined size and use such ability to allocate the minimal size on the ring > buffer to make the entry fit inside as opposite to a fixed length strings with > upper bound. > > This patch provides two new macros: > > -__ending_string(name) > > This one declares the string to the structure inside TP_STRUCT__entry. > Only the name is needed. > Two constraints: only one __ending_string() per TRACE_EVENT can be added and > it must be the last field to be declared. Hence the __ending prefix. > > - open_string_assign(call, dst, src) > > This one does the copy inside TP__fast_assign() of the source > string to the destination. The name of the tracepoint (call) must be provided > for now. Hopefully I will find a solution to avoid it later. > > Two constraint: can be used only once and always on the beginning because > it needs to manage the ring buffer reservation by itself. Hence the open prefix. > > How does it works? > I'll let you know if I meet any problem when using this in blktrace TRACE_EVENTs. > A new has_ending_string field has been added to struct ftrace_event_call and is > false by default. > Once a TRACE_EVENT uses an __ending_string field, it is set to 1. > > Until now, the ring buffer reservation was done in ftrace_raw_event_##call(). > It is still the case if we don't have an __ending_string() field. If we have one, > open_string_assign() will manage it itself to allocate the appropriate size, > depending of the size of the string to be copied for each trace. > > The choice between the usual static allocation and the new dynamic one depends > on the "has_ending_string" value. > > It also support filtering because these strings behave essentially > like usual fixed length string. > > Signed-off-by: Frederic Weisbecker > --- > include/linux/ftrace_event.h | 1 + > include/trace/ftrace.h | 62 ++++++++++++++++++++++++++++++++++++----- > 2 files changed, 55 insertions(+), 8 deletions(-) ... > +/* > + * If we have and ending undefined string size, then the size of > + * the entry is dynamic. In such case we override the ring buffer > + * reservation to manage it ourselves with our dynamic string size. > + */ > +#undef open_string_assign > +#define open_string_assign(call, dst, src) \ > + event = trace_current_buffer_lock_reserve( \ > + event_##call.id, \ > + sizeof(struct ftrace_raw_##call) + strlen(src) + 1, \ > + irq_flags, pc); \ > + if (!event) \ > + return; \ > + entry = ring_buffer_event_data(event); \ small nits, below is better since we have only one assignment: entry = ring_buffer_event_data(event); > + strcpy(entry->dst, src); > + > #undef TRACE_EVENT > #define TRACE_EVENT(call, proto, args, tstruct, assign, print) \ > _TRACE_PROFILE(call, PARAMS(proto), PARAMS(args)) \ > @@ -418,20 +461,23 @@ static struct ftrace_event_call event_##call; \ > static void ftrace_raw_event_##call(proto) \ > { \ > struct ftrace_event_call *call = &event_##call; \ > - struct ring_buffer_event *event; \ > - struct ftrace_raw_##call *entry; \ > + struct ring_buffer_event *event = NULL; \ > + struct ftrace_raw_##call *entry = NULL; \ > unsigned long irq_flags; \ > int pc; \ > \ > local_save_flags(irq_flags); \ > pc = preempt_count(); \ > \ > - event = trace_current_buffer_lock_reserve(event_##call.id, \ > - sizeof(struct ftrace_raw_##call), \ > - irq_flags, pc); \ > - if (!event) \ > - return; \ > - entry = ring_buffer_event_data(event); \ > + if (!call->has_ending_string) { \ > + event = trace_current_buffer_lock_reserve( \ > + event_##call.id, \ > + sizeof(struct ftrace_raw_##call), \ > + irq_flags, pc); \ > + if (!event) \ > + return; \ > + entry = ring_buffer_event_data(event); \ ditoo > + } \ > \ > assign; \ > \