From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:52726) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1faH3O-0000pJ-04 for qemu-devel@nongnu.org; Tue, 03 Jul 2018 04:52:55 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1faH3L-0006gz-F4 for qemu-devel@nongnu.org; Tue, 03 Jul 2018 04:52:54 -0400 Received: from mail.ispras.ru ([83.149.199.45]:34844) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1faH3L-0006gX-6D for qemu-devel@nongnu.org; Tue, 03 Jul 2018 04:52:51 -0400 From: Pavel Dovgalyuk Date: Tue, 03 Jul 2018 11:52:51 +0300 Message-ID: <20180703085250.28380.33220.stgit@pasha-VirtualBox> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Subject: [Qemu-devel] [PATCH] replay: wake up vCPU when replaying List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org Cc: alex.bennee@linaro.org, pbonzini@redhat.com, maria.klimushenkova@ispras.ru, dovgaluk@ispras.ru, pavel.dovgaluk@ispras.ru In record/replay icount mode vCPU thread and iothread synchronize the execution using the checkpoints. vCPU thread processes the virtual timers and iothread processes all others. When iothread wants to wake up sleeping vCPU thread, it sends dummy queued work. Therefore it could be the following sequence of the events in record mode: - IO: sending dummy work - IO: processing timers - CPU: wakeup - CPU: clearing dummy work - CPU: processing virtual timers But due to the races in replay mode the sequence may change: - IO: sending dummy work - CPU: wakeup - CPU: clearing dummy work - CPU: sleeping again because nothing to do - IO: Processing timers - CPU: zzzz In this case vCPU will not wake up, because dummy work is not to be set up again. This patch tries to wake up the vCPU when it sleeps and the icount warp checkpoint isn't met. It means that vCPU has something to do, because there are no other reasons of non-matching warp checkpoint. Signed-off-by: Pavel Dovgalyuk --- cpus.c | 15 ++++++++++----- 1 file changed, 10 insertions(+), 5 deletions(-) diff --git a/cpus.c b/cpus.c index 181ce33..bad6a33 100644 --- a/cpus.c +++ b/cpus.c @@ -539,11 +539,6 @@ void qemu_start_warp_timer(void) return; } - /* warp clock deterministically in record/replay mode */ - if (!replay_checkpoint(CHECKPOINT_CLOCK_WARP_START)) { - return; - } - if (!all_cpu_threads_idle()) { return; } @@ -553,6 +548,16 @@ void qemu_start_warp_timer(void) return; } + /* warp clock deterministically in record/replay mode */ + if (!replay_checkpoint(CHECKPOINT_CLOCK_WARP_START)) { + /* vCPU is sleeping and warp can't be started. + It is probably a race condition: notification sent + to vCPU was processed in advance and vCPU went to sleep. + Therefore we have to wake it up for doing someting. */ + qemu_clock_notify(QEMU_CLOCK_VIRTUAL); + return; + } + /* We want to use the earliest deadline from ALL vm_clocks */ clock = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL_RT); deadline = qemu_clock_deadline_ns_all(QEMU_CLOCK_VIRTUAL);