From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([209.51.188.92]:43670) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1gjgfo-0007bn-MA for qemu-devel@nongnu.org; Wed, 16 Jan 2019 03:35:46 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1gjgfm-00081d-KA for qemu-devel@nongnu.org; Wed, 16 Jan 2019 03:35:44 -0500 Received: from mail-ot1-x331.google.com ([2607:f8b0:4864:20::331]:39855) by eggs.gnu.org with esmtps (TLS1.0:RSA_AES_128_CBC_SHA1:16) (Exim 4.71) (envelope-from ) id 1gjgfk-0007x9-HL for qemu-devel@nongnu.org; Wed, 16 Jan 2019 03:35:42 -0500 Received: by mail-ot1-x331.google.com with SMTP id n8so5890958otl.6 for ; Wed, 16 Jan 2019 00:35:35 -0800 (PST) MIME-Version: 1.0 References: <000601d4a8e8$a8a10170$f9e30450$@ru> <001301d4ad62$f3f44820$dbdcd860$@ru> In-Reply-To: <001301d4ad62$f3f44820$dbdcd860$@ru> From: Artem Pisarenko Date: Wed, 16 Jan 2019 14:35:23 +0600 Message-ID: Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Subject: Re: [Qemu-devel] [PATCH v3 0/4] Introduce attributes for timers subsystem and remove QEMU_CLOCK_VIRTUAL_EXT clock type List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Pavel Dovgalyuk Cc: qemu-devel , Pavel Dovgalyuk , Paolo Bonzini =D1=81=D1=80, 16 =D1=8F=D0=BD=D0=B2. 2019 =D0=B3. =D0=B2 12:15, Pavel Dovga= lyuk : > > > From: Artem Pisarenko [mailto:artem.k.pisarenko@gmail.com] > > > It seems, that this approach is not always correct. > > > Now timerlist_deadline_ns uses all virtual timers for deadline calcul= ation (including > > external > > > ones). > > > qemu_start_warp_timer uses the deadline for setting warp timer (which= should be > > deterministic). > > > Therefore warp timer may become non-deterministic and replay may beha= ve differently compared > > to > > > recording phase. > > > > > > We have to rollback these or improve somehow to avoid non-determinism= . > > > > I dont understand how this approach would even introduce > > non-determinism. I'm not sure about aspects of timers subsystem you > > mentioned, assuming that maybe we missed something when tried to > > optimize. But this has nothing to do with determinism as long as we > > treat all virtual clock timers as deterministic, regardless of > > EXTERNAL attribute being set or not. They are intended to be used as > > such by design, aren't? This attribute was introduced purely to avoid > > extra events in log. > > Right, but deadline calculation and icount warp events (that are written = into the log too) > depend on the active virtual timers. Therefore external ones may affect i= count warp > operation sequence. > > Pavel Dovgalyuk > Sorry, but I still don't understand the source of non-determinism. >>From what you said I may understand that replay module actually has some additional non-trivial (for me) dependencies on EXTERNAL attribute other than one, introduced in 'timerlist_run_timers()' (i.e. it expects deadline calculations somewhere else to match decisions made in this function, or something like that). I would agree that these patch series might introduce some incorrect behavior. But it must be identical in all emulations running in same conditions, because deadline, warp timer and their effects are all dependent only on virtual timers, and, therefore, are deterministic too. Of course, it needs to be fixed. Did you find solution ?