From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.3 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED, USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id D5938C43441 for ; Thu, 22 Nov 2018 13:42:55 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 892592081C for ; Thu, 22 Nov 2018 13:42:55 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="d2whUuXI" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 892592081C Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2436991AbeKWAWQ (ORCPT ); Thu, 22 Nov 2018 19:22:16 -0500 Received: from bombadil.infradead.org ([198.137.202.133]:46528 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2436977AbeKWAWQ (ORCPT ); Thu, 22 Nov 2018 19:22:16 -0500 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20170209; h=In-Reply-To:Content-Type:MIME-Version :References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=1QTzSVO94g0wnOGs1CIZXYdIPuLak3HQX26kKCg76A4=; b=d2whUuXIMoLDUf39ff7wMcgUp zcpi789mE0MNUWbDLkFSUqplnMxoaYWaz9Q9BGHXjSsoJqicNoLgW+y92qxJWMZzwfFTPtqBJkY1a SMDKenxESupZorZdEb3rEjs/VbLTlHMIGSpZHq26d2A0XYRS/WjTfRPFAH7sJpZw/41ibqeXYWHzX nHvQXy9E9eqb1g2mI0bWdWkp5JbkdWlGyPY238HbfDFKk243wHp13ByBCqz53mUOKd1pJG8E4JNsQ qqJdShXqPVLGN1KU2DHurVVwsIJnvuOFX3R1536leZVEB4LYAbufcV7WrKJtbr9EIEmE+JA+qMoxO RR74Mw9OA==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=hirez.programming.kicks-ass.net) by bombadil.infradead.org with esmtpsa (Exim 4.90_1 #2 (Red Hat Linux)) id 1gPpFl-0000fw-E5; Thu, 22 Nov 2018 13:42:45 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id C1F662029FD58; Thu, 22 Nov 2018 14:42:38 +0100 (CET) Date: Thu, 22 Nov 2018 14:42:38 +0100 From: Peter Zijlstra To: Steven Rostedt Cc: linux-kernel@vger.kernel.org, Ingo Molnar , Andrew Morton , Thomas Gleixner , Masami Hiramatsu , Josh Poimboeuf , Frederic Weisbecker , Joel Fernandes , Andy Lutomirski , Mark Rutland Subject: Re: [RFC][PATCH 00/14] function_graph: Rewrite to allow multiple users Message-ID: <20181122134238.GU2131@hirez.programming.kicks-ass.net> References: <20181122012708.491151844@goodmis.org> <20181122100812.GO2131@hirez.programming.kicks-ass.net> <20181122074605.063a7525@vmware.local.home> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181122074605.063a7525@vmware.local.home> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Nov 22, 2018 at 07:46:05AM -0500, Steven Rostedt wrote: > On Thu, 22 Nov 2018 11:08:12 +0100 > Peter Zijlstra wrote: > > > On Wed, Nov 21, 2018 at 08:27:08PM -0500, Steven Rostedt wrote: > > > Well the fuction graph tracer is arguably the strongest of the tracers. > > > It shows both the entrance and exit of a function, can give the timings > > > of a function, and shows the execution of the code quite nicely. > > > > > > But it has one major flaw. > > > > > > It can't let more than one user access it at a time. > > > > The reason I 'never' use it is performance, it _sucks_.. I've never ran > > into the multi-user issue. > > And performance is also something to fix (it has improved lately, you > probably haven't noticed). Indeed, I've not recently used it. > > So while I don't think the rewrite is bad, this argument here is. > > Except that we plan on merging kretprobe with function graph tracing. > This also solves the issue that Mark Rutland has with ret protection. > He has a solution for function graph tracing, but not with kretprobes. Sure. But you didn't make that argument. > And yes, there's also the case of being able to trace to different > buffers where you can have a full function graph tracing enabled and > also trace a subset that you want to have. > > Just because you don't need it, doesn't mean it's not needed by others. Not saying that; just saying the argument doesn't hold. It is not the _one_ flaw.