Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S935188Ab0KQSxd (ORCPT ); Wed, 17 Nov 2010 13:53:33 -0500 Received: from mail-fx0-f46.google.com ([209.85.161.46]:58534 "EHLO mail-fx0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S935069Ab0KQSxc (ORCPT ); Wed, 17 Nov 2010 13:53:32 -0500 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=subject:from:to:cc:in-reply-to:references:content-type:date :message-id:mime-version:x-mailer:content-transfer-encoding; b=Q9fDnw0bnaA5ak3bpGg41J+DFI9DAm4CMmS62KwLmEP4wqZ2+zXxvVjd5eWh9+clNV 0yJAflL+64kfSJmo3vgOLyy2t59aDqTzAtEA04biJNRWdWpR7yx0B6fdx/sXDZqwYrJn fYT1h5y/zJQHSTYPPTXOyEnaKdgOMJNiYfSq0= Subject: Re: [ANNOUNCE] New utility: 'trace' From: Tom Zanussi To: Mathieu Desnoyers Cc: Peter Zijlstra , Ingo Molnar , "Ted Ts'o" , Thomas Gleixner , LKML , Linus Torvalds , Andrew Morton , Steven Rostedt , Arjan van de Ven , Arnaldo Carvalho de Melo , Frederic Weisbecker , Masami Hiramatsu , Li Zefan , Jason Baron , "David S. Miller" , Christoph Hellwig , Pekka Enberg , Lai Jiangshan , Eric Dumazet In-Reply-To: <20101117183642.GE13717@Krystal> References: <20101117013700.GA3290@thunk.org> <20101117132404.GF27063@elte.hu> <1290001128.2109.785.camel@laptop> <20101117140002.GH27063@elte.hu> <1290003110.2109.822.camel@laptop> <1290008001.1921.14.camel@elnicho> <20101117183642.GE13717@Krystal> Content-Type: text/plain; charset="UTF-8" Date: Wed, 17 Nov 2010 12:53:24 -0600 Message-ID: <1290020004.1921.25.camel@elnicho> Mime-Version: 1.0 X-Mailer: Evolution 2.30.3 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2548 Lines: 60 On Wed, 2010-11-17 at 13:36 -0500, Mathieu Desnoyers wrote: > * Tom Zanussi (tzanussi@gmail.com) wrote: > [...] > > IIRC, I think the conclusion we came to was that it could be done > > mechanically if for example the right-hand-side of an assignment in > > TP_fast_assign() only involved a simple variable assignment, but as > > Steve pointed out, some assignments are more complicated than that. > > Yep, we came up to the same conclusions in UST. > > > For example, in the sched_switch tracepoint assignments: > > > > __entry->prev_prio = prev->prio; > > __entry->prev_state = __trace_sched_switch_state(prev); > > > > so the prev_prio should be able to be tested 'in-line' but the > > prev_state would require a temporary buffer to write the value into > > before doing the test as mentioned by Steve. At which point you're no > > further ahead (in that case) than the current situation... > > if we change all assignments to, e.g.: > > _tp_assign(__entry->prev_prio, prev->prio) > _tp_assign(__entry->prev_state, __trace_sched_switch_state(prev)) > > then we can redefine the macros for filtering much more easily than with the > " = " assignment operator. > > About your comment above, what is the problem with evaluating > "__trace_sched_switch_state(prev)" twice ? It will typically be cache-hot after > the first evaluation, so I wonder if, in practice, we really save a significant > amount of cycles by saving its result between filtering and writing into trace > buffers. As I pointed out earlier, for my customers, having a very, very fast > filter "out" case is more important that trying to squeeze a few cycles out of > the filter passed case. > But the idea is to avoid allocating the trace buffer in the first place, until we've decided we want the event. So how do you check the result of __trace_sched_switch_state(prev) with the filter value if you don't have it temporarily stored somewhere (not in the trace buffer, which doesn't exist yet as far as this event is concerned)? Tom > Also, how many of these "__trace_sched_switch_state(prev)" are static inlines vs > actual function calls ? If it's mostly static inlines to dereference a few > pointers, doing it the second time when the filter passed won't hurt much. > > Thanks, > > Mathieu > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/