From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dave Chinner Subject: Re: [PATCH 3/6] dax: add tracepoint infrastructure, PMD tracing Date: Fri, 25 Nov 2016 13:49:18 +1100 Message-ID: <20161125024918.GX31101@dastard> References: <1479926662-21718-1-git-send-email-ross.zwisler@linux.intel.com> <1479926662-21718-4-git-send-email-ross.zwisler@linux.intel.com> <20161124173220.GR1555@ZenIV.linux.org.uk> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: Jan Kara , Andrew Morton , Matthew Wilcox , linux-nvdimm-hn68Rpc1hR1g9hUCZPvPmw@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Steven Rostedt , Christoph Hellwig , linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org, Ingo Molnar , linux-fsdevel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-ext4-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Al Viro Return-path: Content-Disposition: inline In-Reply-To: <20161124173220.GR1555-3bDd1+5oDREiFSDQTTA3OLVCufUGDwFn@public.gmane.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: linux-nvdimm-bounces-hn68Rpc1hR1g9hUCZPvPmw@public.gmane.org Sender: "Linux-nvdimm" List-Id: linux-ext4.vger.kernel.org On Thu, Nov 24, 2016 at 05:32:20PM +0000, Al Viro wrote: > On Wed, Nov 23, 2016 at 11:44:19AM -0700, Ross Zwisler wrote: > > Tracepoints are the standard way to capture debugging and tracing > > information in many parts of the kernel, including the XFS and ext4 > > filesystems. Create a tracepoint header for FS DAX and add the first DAX > > tracepoints to the PMD fault handler. This allows the tracing for DAX to > > be done in the same way as the filesystem tracing so that developers can > > look at them together and get a coherent idea of what the system is doing. > > It also has one hell of potential for becoming a massive nuisance. > Keep in mind that if any userland code becomes dependent on those - that's it, > they have become parts of stable userland ABI and are to be maintained > indefinitely. Don't expect "tracepoints are special case" to prevent that. I call bullshit just like I always do when someone spouts this "tracepoints are stable ABI" garbage. If we want to provide stable tracepoints, then we need to /create a stable tracepoint API/ and convert all the tracepoints that /need to be stable/ to use it. Then developers only need to be careful about modifying code around the /explicitly stable/ tracepoints and we avoid retrospectively locking the kernel implementation into a KABI so tight we can't do anything anymore.... Quite frankly, anyone that wants to stop us from adding/removing/changing tracepoints or the code that they are reporting information about "because ABI" can go take a long walk off a short cliff. Diagnostic tracepoints are not part of the stable ABI. End of story. > So treat anything you add in that manner as potential stable ABI > you might have to keep around forever. It's *not* a glorified debugging > printk. trace_printk() is the glorified debugging printk for tracing, not trace events. Cheers, Dave. -- Dave Chinner david-FqsqvQoI3Ljby3iVrkZq2A@public.gmane.org From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from ipmail05.adl6.internode.on.net (ipmail05.adl6.internode.on.net [150.101.137.143]) by ml01.01.org (Postfix) with ESMTP id 8F30A81C5E for ; Thu, 24 Nov 2016 18:49:22 -0800 (PST) Date: Fri, 25 Nov 2016 13:49:18 +1100 From: Dave Chinner Subject: Re: [PATCH 3/6] dax: add tracepoint infrastructure, PMD tracing Message-ID: <20161125024918.GX31101@dastard> References: <1479926662-21718-1-git-send-email-ross.zwisler@linux.intel.com> <1479926662-21718-4-git-send-email-ross.zwisler@linux.intel.com> <20161124173220.GR1555@ZenIV.linux.org.uk> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20161124173220.GR1555@ZenIV.linux.org.uk> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: linux-nvdimm-bounces@lists.01.org Sender: "Linux-nvdimm" To: Al Viro Cc: Jan Kara , Andrew Morton , Matthew Wilcox , linux-nvdimm@lists.01.org, linux-kernel@vger.kernel.org, Steven Rostedt , Christoph Hellwig , linux-mm@kvack.org, Ingo Molnar , linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org List-ID: On Thu, Nov 24, 2016 at 05:32:20PM +0000, Al Viro wrote: > On Wed, Nov 23, 2016 at 11:44:19AM -0700, Ross Zwisler wrote: > > Tracepoints are the standard way to capture debugging and tracing > > information in many parts of the kernel, including the XFS and ext4 > > filesystems. Create a tracepoint header for FS DAX and add the first DAX > > tracepoints to the PMD fault handler. This allows the tracing for DAX to > > be done in the same way as the filesystem tracing so that developers can > > look at them together and get a coherent idea of what the system is doing. > > It also has one hell of potential for becoming a massive nuisance. > Keep in mind that if any userland code becomes dependent on those - that's it, > they have become parts of stable userland ABI and are to be maintained > indefinitely. Don't expect "tracepoints are special case" to prevent that. I call bullshit just like I always do when someone spouts this "tracepoints are stable ABI" garbage. If we want to provide stable tracepoints, then we need to /create a stable tracepoint API/ and convert all the tracepoints that /need to be stable/ to use it. Then developers only need to be careful about modifying code around the /explicitly stable/ tracepoints and we avoid retrospectively locking the kernel implementation into a KABI so tight we can't do anything anymore.... Quite frankly, anyone that wants to stop us from adding/removing/changing tracepoints or the code that they are reporting information about "because ABI" can go take a long walk off a short cliff. Diagnostic tracepoints are not part of the stable ABI. End of story. > So treat anything you add in that manner as potential stable ABI > you might have to keep around forever. It's *not* a glorified debugging > printk. trace_printk() is the glorified debugging printk for tracing, not trace events. Cheers, Dave. -- Dave Chinner david@fromorbit.com _______________________________________________ Linux-nvdimm mailing list Linux-nvdimm@lists.01.org https://lists.01.org/mailman/listinfo/linux-nvdimm From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Date: Fri, 25 Nov 2016 13:49:18 +1100 From: Dave Chinner To: Al Viro Cc: Ross Zwisler , linux-kernel@vger.kernel.org, Andrew Morton , Christoph Hellwig , Dan Williams , Ingo Molnar , Jan Kara , Matthew Wilcox , Steven Rostedt , linux-ext4@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-nvdimm@lists.01.org Subject: Re: [PATCH 3/6] dax: add tracepoint infrastructure, PMD tracing Message-ID: <20161125024918.GX31101@dastard> References: <1479926662-21718-1-git-send-email-ross.zwisler@linux.intel.com> <1479926662-21718-4-git-send-email-ross.zwisler@linux.intel.com> <20161124173220.GR1555@ZenIV.linux.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20161124173220.GR1555@ZenIV.linux.org.uk> Sender: owner-linux-mm@kvack.org List-ID: On Thu, Nov 24, 2016 at 05:32:20PM +0000, Al Viro wrote: > On Wed, Nov 23, 2016 at 11:44:19AM -0700, Ross Zwisler wrote: > > Tracepoints are the standard way to capture debugging and tracing > > information in many parts of the kernel, including the XFS and ext4 > > filesystems. Create a tracepoint header for FS DAX and add the first DAX > > tracepoints to the PMD fault handler. This allows the tracing for DAX to > > be done in the same way as the filesystem tracing so that developers can > > look at them together and get a coherent idea of what the system is doing. > > It also has one hell of potential for becoming a massive nuisance. > Keep in mind that if any userland code becomes dependent on those - that's it, > they have become parts of stable userland ABI and are to be maintained > indefinitely. Don't expect "tracepoints are special case" to prevent that. I call bullshit just like I always do when someone spouts this "tracepoints are stable ABI" garbage. If we want to provide stable tracepoints, then we need to /create a stable tracepoint API/ and convert all the tracepoints that /need to be stable/ to use it. Then developers only need to be careful about modifying code around the /explicitly stable/ tracepoints and we avoid retrospectively locking the kernel implementation into a KABI so tight we can't do anything anymore.... Quite frankly, anyone that wants to stop us from adding/removing/changing tracepoints or the code that they are reporting information about "because ABI" can go take a long walk off a short cliff. Diagnostic tracepoints are not part of the stable ABI. End of story. > So treat anything you add in that manner as potential stable ABI > you might have to keep around forever. It's *not* a glorified debugging > printk. trace_printk() is the glorified debugging printk for tracing, not trace events. Cheers, Dave. -- Dave Chinner david@fromorbit.com -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752083AbcKYCtf (ORCPT ); Thu, 24 Nov 2016 21:49:35 -0500 Received: from ipmail05.adl6.internode.on.net ([150.101.137.143]:9730 "EHLO ipmail05.adl6.internode.on.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751439AbcKYCtY (ORCPT ); Thu, 24 Nov 2016 21:49:24 -0500 X-IronPort-Anti-Spam-Filtered: true X-IronPort-Anti-Spam-Result: A2A1CgD7pTdYIFo9LHldHAEBBAEBCgEBgzgBAQEBAR+BWoJ7g3mcRgaBHYwphj2CDoIIhhsEAgKBd0ETAQIBAQEBAQEBBgEBAQEBATgBRYRoAQEBAwE6HCMFCwgDGAklDwUlAwcaE4hlB64gi00BAQgCJSCFVIUliioFmlSQeZA/jXGEDB8BgSoTDIVlKjSINwEBAQ Date: Fri, 25 Nov 2016 13:49:18 +1100 From: Dave Chinner To: Al Viro Cc: Ross Zwisler , linux-kernel@vger.kernel.org, Andrew Morton , Christoph Hellwig , Dan Williams , Ingo Molnar , Jan Kara , Matthew Wilcox , Steven Rostedt , linux-ext4@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-nvdimm@ml01.01.org Subject: Re: [PATCH 3/6] dax: add tracepoint infrastructure, PMD tracing Message-ID: <20161125024918.GX31101@dastard> References: <1479926662-21718-1-git-send-email-ross.zwisler@linux.intel.com> <1479926662-21718-4-git-send-email-ross.zwisler@linux.intel.com> <20161124173220.GR1555@ZenIV.linux.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20161124173220.GR1555@ZenIV.linux.org.uk> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Nov 24, 2016 at 05:32:20PM +0000, Al Viro wrote: > On Wed, Nov 23, 2016 at 11:44:19AM -0700, Ross Zwisler wrote: > > Tracepoints are the standard way to capture debugging and tracing > > information in many parts of the kernel, including the XFS and ext4 > > filesystems. Create a tracepoint header for FS DAX and add the first DAX > > tracepoints to the PMD fault handler. This allows the tracing for DAX to > > be done in the same way as the filesystem tracing so that developers can > > look at them together and get a coherent idea of what the system is doing. > > It also has one hell of potential for becoming a massive nuisance. > Keep in mind that if any userland code becomes dependent on those - that's it, > they have become parts of stable userland ABI and are to be maintained > indefinitely. Don't expect "tracepoints are special case" to prevent that. I call bullshit just like I always do when someone spouts this "tracepoints are stable ABI" garbage. If we want to provide stable tracepoints, then we need to /create a stable tracepoint API/ and convert all the tracepoints that /need to be stable/ to use it. Then developers only need to be careful about modifying code around the /explicitly stable/ tracepoints and we avoid retrospectively locking the kernel implementation into a KABI so tight we can't do anything anymore.... Quite frankly, anyone that wants to stop us from adding/removing/changing tracepoints or the code that they are reporting information about "because ABI" can go take a long walk off a short cliff. Diagnostic tracepoints are not part of the stable ABI. End of story. > So treat anything you add in that manner as potential stable ABI > you might have to keep around forever. It's *not* a glorified debugging > printk. trace_printk() is the glorified debugging printk for tracing, not trace events. Cheers, Dave. -- Dave Chinner david@fromorbit.com