From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:54337) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ae0VE-0000aT-4L for qemu-devel@nongnu.org; Thu, 10 Mar 2016 08:19:45 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ae0V8-0007C4-2Z for qemu-devel@nongnu.org; Thu, 10 Mar 2016 08:19:44 -0500 Received: from mail.ispras.ru ([83.149.199.45]:56537) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ae0V7-0007Br-MU for qemu-devel@nongnu.org; Thu, 10 Mar 2016 08:19:37 -0500 From: "Pavel Dovgalyuk" References: <20160310115551.4812.55431.stgit@PASHA-ISP> <20160310115609.4812.44986.stgit@PASHA-ISP> <56E1642A.4080407@redhat.com> In-Reply-To: <56E1642A.4080407@redhat.com> Date: Thu, 10 Mar 2016 16:19:30 +0300 Message-ID: <000e01d17acf$7b1c3480$71549d80$@ru> MIME-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Content-Language: ru Subject: Re: [Qemu-devel] [PATCH v4 3/5] icount: decouple warp calls List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: 'Paolo Bonzini' , 'Pavel Dovgalyuk' , qemu-devel@nongnu.org Cc: edgar.iglesias@xilinx.com, peter.maydell@linaro.org, igor.rubinov@gmail.com, mark.burton@greensocs.com, real@ispras.ru, batuzovk@ispras.ru, maria.klimushenkova@ispras.ru, stefanha@redhat.com, kwolf@redhat.com, hines@cert.org, alex.bennee@linaro.org, fred.konrad@greensocs.com > From: Paolo Bonzini [mailto:pbonzini@redhat.com] > On 10/03/2016 12:56, Pavel Dovgalyuk wrote: > > qemu_clock_warp function is called to update virtual clock when CPU > > is sleeping. This function includes replay checkpoint to make execution > > deterministic in icount mode. > > Record/replay module flushes async event queue at checkpoints. > > Some of the events (e.g., block devices operations) include interaction > > with hardware. E.g., APIC polled by block devices sets one of IRQ flags. > > Flag to be set depends on currently executed thread (CPU or iothread). > > Therefore in replay mode we have to process the checkpoints in the same thread > > as they were recorded. > > qemu_clock_warp function (and its checkpoint) may be called from different > > thread. This patch decouples two different execution cases of this function: > > call when CPU is sleeping from iothread and call from cpu thread to update > > virtual clock. > > First task is performed by qemu_start_warp_timer function. It sets warp > > timer event to the moment of nearest pending virtual timer. > > Second function (qemu_account_warp_timer) is called from cpu thread > > before execution of the code. It advances virtual clock by adding the length > > of period while CPU was sleeping. > > > > Signed-off-by: Pavel Dovgalyuk > > Lovely. :) One question, why doesn't icount_dummy_timer need a checkpoint? It is synchronized with CHECKPOINT_CLOCK_VIRTUAL_RT. > Only needs a change to the documentation: Ok, I'll change it. > > diff --git a/docs/replay.txt b/docs/replay.txt > index 149727e..26dfb6e 100644 > --- a/docs/replay.txt > +++ b/docs/replay.txt > @@ -134,11 +134,18 @@ of time. That's why we do not process a group of timers until the > checkpoint > event will be read from the log. Such an event allows synchronizing CPU > execution and timer events. > > -Another checkpoints application in record/replay is instruction counting > -while the virtual machine is idle. This function (qemu_clock_warp) is called > -from the wait loop. It changes virtual machine state and must be deterministic > -then. That is why we added checkpoint to this function to prevent its > -operation in replay mode when it does not correspond to record mode. > +Two other checkpoints govern the "warping" of the virtual clock. While > +the virtual machine is idle, the virtual clock increments at 1 ns per > +*real time* nanosecond. This is done by setting up a timer (called the > +warp timer) and then incrementing the virtual clock (called "warping" > +the virtual clock) as soon as the CPUs need to go out of the idle state. > +These actions change virtual machine state and must be deterministic. > +Two functions are used for this purpose, and each of them creates a > +checkpoint. qemu_start_warp_timer checks if the CPUs are idle and if so > +starts accounting real time to virtual clock. qemu_account_warp_timer > +is called when the CPUs get an interrupt or when a virtual clock timer > +fires, and it warps the virtual clock by the amount of real time that > +has passed since qemu_start_warp_timer. Pavel Dovgalyuk