From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from [140.186.70.92] (port=38884 helo=eggs.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1P8CNE-0005KO-LS for qemu-devel@nongnu.org; Tue, 19 Oct 2010 09:37:05 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1P8CND-0006lV-Av for qemu-devel@nongnu.org; Tue, 19 Oct 2010 09:37:04 -0400 Received: from mx1.redhat.com ([209.132.183.28]:65358) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1P8CND-0006lN-3c for qemu-devel@nongnu.org; Tue, 19 Oct 2010 09:37:03 -0400 Date: Tue, 19 Oct 2010 14:36:59 +0100 From: "Daniel P. Berrange" Subject: Re: [Qemu-devel] Static tracepoint control via trace-event Message-ID: <20101019133659.GH23535@redhat.com> References: <4CBD9838.6040004@siemens.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4CBD9838.6040004@siemens.com> Reply-To: "Daniel P. Berrange" List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Jan Kiszka Cc: Stefan Hajnoczi , qemu-devel On Tue, Oct 19, 2010 at 03:08:08PM +0200, Jan Kiszka wrote: > Hi Stefan, > > just had a closer look at qemu's new tracing framework. Looks cool, > though it leaves a bit room for improvements. ;) > > One quirk I stumbled over quickly was the "disable" tag in trace-events. > It confused me first as qemu starts without any tracepoint enabled by > default and I thought I had to hack the file. Then I read the doc and > wondered which exiting or future backend would come without sufficiently > fast dynamic tracepoint control. Do you have any in mind? > > Instead of making it a compile-time switch (except for simpletrace), I > would vote for declaring the simpletrace usage as the only one: disable > sets the default state of the dynamic tracepoint. That way we could use > trace-events to define a useful set of standard, moderate-impact > tracepoints that shall be on. Others will still be available once a > backend is configured, but remain off until enabled during runtime. > Anything else looks like overkill to me. FYI with the DTrace/SystemTAP backend I posted yesterday, the 'disable' keyword is effectively completely ignored. All tracepoints are disabled when QEMU is running normally. Only when a end user runs a dtrace script that references a QEMU tracepoint, is that specific tracepoint enabled. Regards, Daniel -- |: Red Hat, Engineering, London -o- http://people.redhat.com/berrange/ :| |: http://libvirt.org -o- http://virt-manager.org -o- http://deltacloud.org :| |: http://autobuild.org -o- http://search.cpan.org/~danberr/ :| |: GnuPG: 7D3B9505 -o- F3C9 553F A1DA 4AC2 5648 23C1 B3DF F742 7D3B 9505 :|