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Mon, 3 Aug 2020 11:54:39 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id 8E9711132FD2; Mon, 3 Aug 2020 13:54:37 +0200 (CEST) From: Markus Armbruster To: Stefan Hajnoczi Subject: Re: [PATCH v4 2/2] trace: Example of non-tracing recorder use References: <20200723132903.1980743-1-dinechin@redhat.com> <20200723132903.1980743-3-dinechin@redhat.com> <20200803104432.GG244853@stefanha-x1.localdomain> Date: Mon, 03 Aug 2020 13:54:37 +0200 In-Reply-To: <20200803104432.GG244853@stefanha-x1.localdomain> (Stefan Hajnoczi's message of "Mon, 3 Aug 2020 11:44:32 +0100") Message-ID: <87d048j66a.fsf@dusky.pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.3 (gnu/linux) MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=armbru@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain Received-SPF: pass client-ip=207.211.31.81; envelope-from=armbru@redhat.com; helo=us-smtp-delivery-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/08/03 02:37:52 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -30 X-Spam_score: -3.1 X-Spam_bar: --- X-Spam_report: (-3.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Christophe de Dinechin , Michael Tokarev , Laurent Vivier , "Dr. David Alan Gilbert" , qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Stefan Hajnoczi writes: > On Thu, Jul 23, 2020 at 03:29:03PM +0200, Christophe de Dinechin wrote: >> This patch is a simple example showing how the recorder can be used to >> have one "topic" covering multiple entries. Here, the topic is "lock", >> the idea being to have the latest lock changes for instance in case of >> a crash or hang. >> >> Here are a few use cases: >> >> * Tracing lock updates: >> RECORDER_TRACES=lock qemu >> * Showing lock changes prior to a hang >> RECORDER_TRACES=lock qemu & >> # Wait until hang >> killall -USR2 qemu # This will trigger a dump >> * Graphic visualization of lock states: >> RECORDER_TRACES="lock=state,id" qemu & >> recorder_scope state >> # Hit the 't' key to toggle timing display >> # Hit the 'c' key to dump the screen data as CSV >> cat recorder_scope_data-1.csv > > Dan raised a good point regarding integrating recorder functionality > behind the tracetool interface. > > On the other hand, I would like to see where this goes so that we have > enough experience to design the tracetool interface, if necessary. > > Therefore I am for merging this as-is and taking action when it's clear > that duplication is taking place. Sounds like we should not yet commit to a stable external interface. The monitor command is HMP only. Not a stable interface. A QMP command would have to be marked experimental with the customary x- prefix. The environment variable is an external interface of the recorder library. Attempting to police such interfaces of libraries we use seems futile.