From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:51083) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1db5uX-0008Qi-ON for qemu-devel@nongnu.org; Fri, 28 Jul 2017 10:06:39 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1db5uU-0005E8-16 for qemu-devel@nongnu.org; Fri, 28 Jul 2017 10:06:37 -0400 Received: from mx1.redhat.com ([209.132.183.28]:35624) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1db5uT-0005Cb-OO for qemu-devel@nongnu.org; Fri, 28 Jul 2017 10:06:33 -0400 Date: Fri, 28 Jul 2017 15:06:23 +0100 From: "Daniel P. Berrange" Message-ID: <20170728140623.GQ31495@redhat.com> Reply-To: "Daniel P. Berrange" References: <20170726112633.GE18489@stefanha-x1.localdomain> <20170727104302.GI2555@redhat.com> <20170727152137.GW2555@redhat.com> <20170727154535.GY2555@redhat.com> <20170728133430.GS12364@stefanha-x1.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: Content-Transfer-Encoding: quoted-printable Subject: Re: [Qemu-devel] [PATCH 00/13] instrument: Add basic event instrumentation List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Peter Maydell Cc: Stefan Hajnoczi , Stefan Hajnoczi , "Emilio G. Cota" , =?utf-8?B?TGx1w61z?= Vilanova , QEMU Developers On Fri, Jul 28, 2017 at 02:41:19PM +0100, Peter Maydell wrote: > On 28 July 2017 at 14:34, Stefan Hajnoczi wrote: > > Llu=C3=ADs/Peter: What are the requirements for instrumentation code > > interacting with the running QEMU instance? simpletrace is > > asynchronous, meaning it does not wait for anyone handle the trace ev= ent > > before continuing execution, and is therefore not suitable for > > SystemTap-style scripts that can interact with the program while > > handling a trace event. >=20 > I think you'd probably want synchronous -- it's pretty helpful > to be able to say "register a trace event hook that doesn't > fire very often, and use that to get to the region of > execution that's of interest to you, then enable more hooks > to get more detail at that point". (For instance, "wait til > we've executed 5,000,000 instructions, then turn on the > tracing of all instruction execution, register modification > and memory accesses".) Currently simpletrace probes have a fixed action when they are enabled, namely to print state to the trace log file. Perhaps we can make the action more flexible, if we create a more formal protocol for simpletrace to let it talk over a UNIX socket. By default it could send probe data asynchronously as now, but you could mark probes such that they require a synchronous ACK, thus pausing execution until that ACK is received from the instrumenting program. For that to be useful, we would need to have allow probes to be turned on/off via this trace socket, since the normal HMP/QMP monitor execution would be blocked while this probe is running. Regards, Daniel --=20 |: https://berrange.com -o- https://www.flickr.com/photos/dberran= ge :| |: https://libvirt.org -o- https://fstop138.berrange.c= om :| |: https://entangle-photo.org -o- https://www.instagram.com/dberran= ge :|