From: "Pavel Dovgalyuk" <dovgaluk@ispras.ru>
To: 'Kevin Wolf' <kwolf@redhat.com>
Cc: edgar.iglesias@xilinx.com, peter.maydell@linaro.org,
igor.rubinov@gmail.com, mark.burton@greensocs.com,
real@ispras.ru, hines@cert.org, qemu-devel@nongnu.org,
maria.klimushenkova@ispras.ru, stefanha@redhat.com,
pbonzini@redhat.com, batuzovk@ispras.ru, alex.bennee@linaro.org,
fred.konrad@greensocs.com
Subject: Re: [Qemu-devel] [PATCH 3/3] replay: introduce block devices record/replay
Date: Wed, 24 Feb 2016 14:59:11 +0300 [thread overview]
Message-ID: <002101d16efa$c74b3850$55e1a8f0$@ru> (raw)
In-Reply-To: <20160222110644.GD5387@noname.str.redhat.com>
> From: Kevin Wolf [mailto:kwolf@redhat.com]
> Am 20.02.2016 um 08:11 hat Pavel Dovgalyuk geschrieben:
> > > From: Pavel Dovgalyuk [mailto:dovgaluk@ispras.ru]
> > > > From: Kevin Wolf [mailto:kwolf@redhat.com]
> > > > Am 16.02.2016 um 12:20 hat Pavel Dovgalyuk geschrieben:
> > > > > Coroutine Replay
> > > > > bool *done = req_replayed_list_get(reqid) // NULL
> > > > > co =
> > > > req_completed_list_get(e.reqid); // NULL
> > > >
> > > > There was no yield, this context switch is impossible to happen. Same
> > > > for the switch back.
> > > >
> > > > > req_completed_list_insert(reqid, qemu_coroutine_self());
> > > > > qemu_coroutine_yield();
> > > >
> > > > This is the point at which a context switch happens. The only other
> > > > point in my code is the qemu_coroutine_enter() in the other function.
> > >
> > > I've fixed aio_poll problem by disabling mutex lock for the replay_run_block_event()
> > > execution. Now virtual machine deterministically runs 4e8 instructions of Windows XP
> booting.
> > > But then one non-deterministic event happens.
> > > Callback after finishing coroutine may be called from different contexts.
>
> How does this happen? I'm not aware of callbacks being processed by any
> thread other than the I/O thread for that specific block device (unless
> you use dataplane, this is the main loop thread).
>
> > > apic_update_irq() function behaves differently being called from vcpu and io threads.
> > > In one case it sets CPU_INTERRUPT_POLL and in other - nothing happens.
> >
> > Kevin, do you have some ideas how to fix this issue?
> > This happens because of coroutines may be assigned to different threads.
> > Maybe there is some way of making this assignment more deterministic?
>
> Coroutines aren't randomly assigned to threads, but threads actively
> enter coroutines. To my knowledge this happens only when starting a
> request (either vcpu or I/O thread; consistent per device) or by a
> callback when some event happens (only I/O thread). I can't see any
> non-determinism here.
Behavior of coroutines looks strange for me.
Consider the code below (co_readv function of the replay driver).
In record mode it somehow changes the thread it assigned to.
Code in point A is executed in CPU thread and code in point B - in some other thread.
May this happen because this coroutine yields somewhere and its execution is restored
by aio_poll, which is called from iothread?
In this case event finishing callback cannot be executed deterministically
(always in CPU thread or always in IO thread).
static int coroutine_fn blkreplay_co_readv(BlockDriverState *bs,
int64_t sector_num, int nb_sectors, QEMUIOVector *qiov)
{
BDRVBlkreplayState *s = bs->opaque;
uint32_t reqid = request_id++;
Request *req;
// A
bdrv_co_readv(bs->file->bs, sector_num, nb_sectors, qiov);
if (replay_mode == REPLAY_MODE_RECORD) {
replay_save_block_event(reqid);
} else {
assert(replay_mode == REPLAY_MODE_PLAY);
if (reqid == current_request) {
current_finished = true;
} else {
req = block_request_insert(reqid, bs, qemu_coroutine_self());
qemu_coroutine_yield();
block_request_remove(req);
}
}
// B
return 0;
}
Pavel Dovgalyuk
next prev parent reply other threads:[~2016-02-24 11:59 UTC|newest]
Thread overview: 46+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-02-09 5:55 [Qemu-devel] [PATCH 0/3] Deterministic replay extensions Pavel Dovgalyuk
2016-02-09 5:55 ` [Qemu-devel] [PATCH 1/3] replay: character devices Pavel Dovgalyuk
2016-02-09 5:55 ` [Qemu-devel] [PATCH 2/3] replay: introduce new checkpoint for icount warp Pavel Dovgalyuk
2016-02-09 5:55 ` [Qemu-devel] [PATCH 3/3] replay: introduce block devices record/replay Pavel Dovgalyuk
2016-02-09 10:27 ` Kevin Wolf
2016-02-09 11:52 ` Pavel Dovgalyuk
2016-02-10 11:45 ` Kevin Wolf
2016-02-10 12:05 ` Pavel Dovgalyuk
2016-02-10 12:28 ` Kevin Wolf
2016-02-10 12:51 ` Pavel Dovgalyuk
2016-02-10 13:25 ` Kevin Wolf
2016-02-10 13:33 ` Pavel Dovgalyuk
2016-02-10 13:52 ` Kevin Wolf
2016-02-11 6:05 ` Pavel Dovgalyuk
2016-02-11 9:43 ` Kevin Wolf
2016-02-11 11:00 ` Pavel Dovgalyuk
2016-02-11 12:18 ` Kevin Wolf
2016-02-11 12:24 ` Pavel Dovgalyuk
2016-02-12 8:33 ` Pavel Dovgalyuk
2016-02-12 9:44 ` Kevin Wolf
2016-02-12 13:19 ` Pavel Dovgalyuk
2016-02-12 13:58 ` Kevin Wolf
2016-02-15 8:38 ` Pavel Dovgalyuk
2016-02-15 9:10 ` Kevin Wolf
2016-02-15 9:14 ` Pavel Dovgalyuk
2016-02-15 9:38 ` Kevin Wolf
2016-02-15 11:19 ` Pavel Dovgalyuk
2016-02-15 12:46 ` Kevin Wolf
2016-02-15 13:54 ` Pavel Dovgalyuk
2016-02-15 14:06 ` Kevin Wolf
2016-02-15 14:24 ` Pavel Dovgalyuk
2016-02-15 15:01 ` Kevin Wolf
2016-02-16 6:25 ` Pavel Dovgalyuk
2016-02-16 10:02 ` Kevin Wolf
2016-02-16 11:20 ` Pavel Dovgalyuk
2016-02-16 12:54 ` Kevin Wolf
2016-02-18 9:18 ` Pavel Dovgalyuk
2016-02-20 7:11 ` Pavel Dovgalyuk
2016-02-22 11:06 ` Kevin Wolf
2016-02-24 11:59 ` Pavel Dovgalyuk [this message]
2016-02-24 13:14 ` Kevin Wolf
2016-02-25 9:06 ` Pavel Dovgalyuk
2016-02-26 9:01 ` Kevin Wolf
2016-02-29 7:03 ` Pavel Dovgalyuk
2016-02-29 7:54 ` Kevin Wolf
2016-02-15 14:50 ` Pavel Dovgalyuk
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