From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756664AbZDPBd1 (ORCPT ); Wed, 15 Apr 2009 21:33:27 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751722AbZDPBdS (ORCPT ); Wed, 15 Apr 2009 21:33:18 -0400 Received: from hrndva-omtalb.mail.rr.com ([71.74.56.123]:50506 "EHLO hrndva-omtalb.mail.rr.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751294AbZDPBdR (ORCPT ); Wed, 15 Apr 2009 21:33:17 -0400 Date: Wed, 15 Apr 2009 21:33:15 -0400 (EDT) From: Steven Rostedt X-X-Sender: rostedt@gandalf.stny.rr.com To: Frederic Weisbecker cc: Ingo Molnar , Zhaolei , Tom Zanussi , Li Zefan , KOSAKI Motohiro , LKML , Peter Zijlstra Subject: Re: [RFC][PATCH 1/2] tracing/events: provide string with undefined size support In-Reply-To: <1239838050-8567-1-git-send-email-fweisbec@gmail.com> Message-ID: References: <1239838050-8567-1-git-send-email-fweisbec@gmail.com> User-Agent: Alpine 2.00 (DEB 1167 2008-08-23) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 16 Apr 2009, Frederic Weisbecker wrote: > Impact: less memory usage for tracing > > This patch provides the support for dynamic size strings on > event tracing. > > 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? > > 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. And I thought I was the only one that could master CPP wackiness ;-) BTW, I was confused on IRC, because I was thinking this was printf like, but no, we only need to be concerned about a string. But I have another idea: > > Signed-off-by: Frederic Weisbecker > --- > include/linux/ftrace_event.h | 1 + > include/trace/ftrace.h | 62 ++++++++++++++++++++++++++++++++++++----- > 2 files changed, 55 insertions(+), 8 deletions(-) > > diff --git a/include/linux/ftrace_event.h b/include/linux/ftrace_event.h > index 75f3ac0..b49bfbf 100644 > --- a/include/linux/ftrace_event.h > +++ b/include/linux/ftrace_event.h > @@ -100,6 +100,7 @@ struct ftrace_event_call { > int n_preds; > struct filter_pred **preds; > void *mod; > + bool has_ending_string; > > #ifdef CONFIG_EVENT_PROFILE > atomic_t profile_count; > diff --git a/include/trace/ftrace.h b/include/trace/ftrace.h > index 60c5323..8ea750e 100644 > --- a/include/trace/ftrace.h > +++ b/include/trace/ftrace.h > @@ -27,6 +27,9 @@ > #undef __field > #define __field(type, item) type item; > > +#undef __ending_string > +#define __ending_string(item) char item[]; > + > #undef TP_STRUCT__entry > #define TP_STRUCT__entry(args...) args > > @@ -146,12 +149,23 @@ ftrace_raw_output_##call(struct trace_iterator *iter, int flags) \ > if (!ret) \ > return 0; > > +#undef __ending_string > +#define __ending_string(item) \ > + ret = trace_seq_printf(s, "\tfield: char " #item "[];\t" \ > + "offset:%u;\n", \ > + (unsigned int)offsetof(typeof(field), item)); \ > + if (!ret) \ > + return 0; > + > #undef __entry > #define __entry REC > > #undef TP_printk > #define TP_printk(fmt, args...) "%s, %s\n", #fmt, __stringify(args) > > +#undef open_string_assign > +#define open_string_assign(call, dst, src) strcpy(__entry->dst, src) > + > #undef TP_fast_assign > #define TP_fast_assign(args...) args > > @@ -189,6 +203,19 @@ ftrace_format_##call(struct trace_seq *s) \ > if (ret) \ > return ret; > > +/* > + * We choose a size of MAX_FILTER_STR_VAL, then we behave like > + * a usual string with the maximum size to keep being filterable. > + */ > +#undef __ending_string > +#define __ending_string(item) \ > + ret = trace_define_field(event_call, "char []", #item, \ > + offsetof(typeof(field), item), \ > + MAX_FILTER_STR_VAL); \ > + if (ret) \ > + return ret; \ > + event_call->has_ending_string = true; > + > #undef TRACE_EVENT > #define TRACE_EVENT(call, proto, args, tstruct, func, print) \ > int \ > @@ -409,6 +436,22 @@ __attribute__((section("_ftrace_events"))) event_##call = { \ > #undef __entry > #define __entry entry > > +/* > + * 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); \ > + 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); \ > + } \ > \ > assign; \ > \ We can get rid of the has_ending_string and open_string_assign and have this: TP_STRUCT__entry( __field(unsigned long, wait_usec) __field(unsigned long, wait_nsec_rem) __ending_string(name) ), TP_fast_assign( __entry->wait_nsec_rem = do_div(waittime, NSEC_PER_USEC); __entry->wait_usec = (unsigned long) waittime; strcpy(__entry->name, lock->name); ), Then we could do the following in the print the assign: #undef __field #define __field(a,b) #undef __array #define __array(a,b,c) #undef __ending_sting #define __ending_string(name) __str_size__ += strlen(name) + 1; #define TRACE_EVENT(call, proto, args, tstruct, assign, print) static void ftrace_raw_event_##call(proto) { int __str_size__ = 0; tstruct event = trace_current_buffer_lock_reserve(event_##call.id, sizeof(struct ftrace_raw_##call) + __str_size__, irq_flags, pc) if (!event) return; entry = ring_buffer_event_data(event); assign } Yes, I did not add other declarations nor the backslashes for the macro, but you get what I'm doing, right? -- Steve