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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 10AF5C433F5 for ; Fri, 22 Apr 2022 11:10:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1385078AbiDVLMv (ORCPT ); Fri, 22 Apr 2022 07:12:51 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33474 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1447049AbiDVLMm (ORCPT ); Fri, 22 Apr 2022 07:12:42 -0400 Received: from desiato.infradead.org (desiato.infradead.org [IPv6:2001:8b0:10b:1:d65d:64ff:fe57:4e05]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D61865622C for ; Fri, 22 Apr 2022 04:09:48 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=desiato.20200630; 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; bh=AGKq+PyA9mo8Ay12CxWSRyAIOyUJ7wvIv5RuoItVCRc=; b=e9qnxNqh4OFX9wncCbqzr1BvPn czcs4J3+MB/STpGvYLgtFv1INvPUBLtZsa0QFq3Kl7byLfjcsLPLuu4VdOi303mJJIgyLVyTwXy3S QfQglHjg72c8HJgXZuiGliV0Nlwuxa/NujdddQKfMaRidLsJg055aDJ+rZbdaw/LzuI8qzKcvL7ld 388IE7nT5SEqqi4R+cicz+V0/y1sL8L35klxp+pl2jMuBF8QSnqWmt1Hxuzh28ZBxK/CUv1IAzFgt jM9FIuNe646B4NzutPs10kJBe1eysUdZpCyqDLbEUIc5WrdY5VcxiarID7jSzaDuEfvCKAxBJ0S8Z mZdu5yXA==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=worktop.programming.kicks-ass.net) by desiato.infradead.org with esmtpsa (Exim 4.94.2 #2 (Red Hat Linux)) id 1nhr9u-007ftu-9S; Fri, 22 Apr 2022 11:09:06 +0000 Received: by worktop.programming.kicks-ass.net (Postfix, from userid 1000) id 0683A9861AB; Fri, 22 Apr 2022 13:09:04 +0200 (CEST) Date: Fri, 22 Apr 2022 13:09:03 +0200 From: Peter Zijlstra To: Delyan Kratunov Cc: "valentin.schneider@arm.com" , "bigeasy@linutronix.de" , "dietmar.eggemann@arm.com" , "keescook@chromium.org" , "andrii@kernel.org" , "vincent.guittot@linaro.org" , "akpm@linux-foundation.org" , "mingo@kernel.org" , "linux-kernel@vger.kernel.org" , "rdunlap@infradead.org" , "rostedt@goodmis.org" , "Kenta.Tada@sony.com" , "adharmap@quicinc.com" , "tglx@linutronix.de" , "bristot@redhat.com" , "ebiederm@xmission.com" , "ast@kernel.org" , "legion@kernel.org" , "ed.tsai@mediatek.com" , "u.kleine-koenig@pengutronix.de" , "juri.lelli@redhat.com" , "x86@kernel.org" Subject: Re: [PATCH] sched/tracing: append prev_state to tp args instead Message-ID: <20220422110903.GW2731@worktop.programming.kicks-ass.net> References: <20220120162520.570782-1-valentin.schneider@arm.com> <93a20759600c05b6d9e4359a1517c88e06b44834.camel@fb.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <93a20759600c05b6d9e4359a1517c88e06b44834.camel@fb.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Apr 21, 2022 at 10:12:25PM +0000, Delyan Kratunov wrote: > Hi folks, > > While working on bpf tooling, we noticed that the sched_switch tracepoint > signature recently changed in an incompatible manner. This affects the > runqslower tools in the kernel tree, as well as multiple libbpf tools in iovisor/bcc. > > It would be a fair amount of churn to fix all these tools, not to mention any > non-public tools people may be using. So on the one hand, too bad, deal with it. None of this is ABI. > If you are open to it, here's a > description and a patch that moves the new argument to the end, > so existing tools can continue working without change (the new argument > just won't be extracted in existing programs): And on the other hand; those users need to be fixed anyway, right? Accessing prev->__state is equally broken. Yes, the proposed hack is cute, but I have very little sympathy for any of this. These are in-kernel interfaces, they change, there must not be any impediment to change. If bpf wants to ride on them, it needs to suffer the pain of doing so.