Re: [Qemu-devel] [RFC PATCH v8 11/21] replay: recording and replaying clock ticks

[Paolo Bonzini <pbonzini@redhat.com>]

On 03/02/2015 11:51, Pavel Dovgaluk wrote:
>> From: Paolo Bonzini [mailto:pbonzini@redhat.com]
>> On 22/01/2015 09:52, Pavel Dovgalyuk wrote:
>>> Clock ticks are considered as the sources of non-deterministic data for
>>> virtual machine. This patch implements saving the clock values when they
>>> are acquired (virtual, host clock, rdtsc, and some other timers).
>>> When replaying the execution corresponding values are read from log and
>>> transfered to the module, which wants to read the values.
>>> Such a design required the clock polling to be synchronized. Sometimes
>>> it is not true - e.g. when timeouts for timer lists are checked. In this case
>>> we use a cached value of the clock, passing it to the client code.
>>>
>>> Signed-off-by: Pavel Dovgalyuk <pavel.dovgaluk@ispras.ru>
>>> ---
>>>  cpus.c                   |    3 +-
>>>  include/qemu/timer.h     |   10 +++++
>>>  qemu-timer.c             |    7 ++--
>>>  replay/Makefile.objs     |    1 +
>>>  replay/replay-internal.h |   13 +++++++
>>>  replay/replay-time.c     |   84 ++++++++++++++++++++++++++++++++++++++++++++++
>>>  replay/replay.h          |   25 ++++++++++++++
>>>  stubs/replay.c           |    9 +++++
>>>  8 files changed, 147 insertions(+), 5 deletions(-)
>>>  create mode 100755 replay/replay-time.c
>>>
>>> diff --git a/cpus.c b/cpus.c
>>> index 8787277..01d89aa 100644
>>> --- a/cpus.c
>>> +++ b/cpus.c
>>> @@ -353,7 +353,8 @@ static void icount_warp_rt(void *opaque)
>>>
>>>      seqlock_write_lock(&timers_state.vm_clock_seqlock);
>>>      if (runstate_is_running()) {
>>> -        int64_t clock = cpu_get_clock_locked();
>>> +        int64_t clock = REPLAY_CLOCK(REPLAY_CLOCK_VIRTUAL_RT,
>>> +                                     cpu_get_clock_locked());
>>>          int64_t warp_delta;
>>>
>>>          warp_delta = clock - vm_clock_warp_start;
>>> diff --git a/include/qemu/timer.h b/include/qemu/timer.h
>>> index 0666920..0c2472c 100644
>>> --- a/include/qemu/timer.h
>>> +++ b/include/qemu/timer.h
>>> @@ -4,6 +4,7 @@
>>>  #include "qemu/typedefs.h"
>>>  #include "qemu-common.h"
>>>  #include "qemu/notify.h"
>>> +#include "replay/replay.h"
>>>
>>>  /* timers */
>>>
>>> @@ -760,6 +761,8 @@ int64_t cpu_icount_to_ns(int64_t icount);
>>>  /*******************************************/
>>>  /* host CPU ticks (if available) */
>>>
>>> +#define cpu_get_real_ticks cpu_get_real_ticks_impl
>>> +
>>>  #if defined(_ARCH_PPC)
>>>
>>>  static inline int64_t cpu_get_real_ticks(void)
>>> @@ -913,6 +916,13 @@ static inline int64_t cpu_get_real_ticks (void)
>>>  }
>>>  #endif
>>>
>>> +#undef cpu_get_real_ticks
>>> +
>>> +static inline int64_t cpu_get_real_ticks(void)
>>
>> cpu_get_real_ticks should never be used.  Please instead wrap
>> cpu_get_ticks() with REPLAY_CLOCK.
> 
> I don't quite understand this comment.
> Do you mean that I should move REPLAY_CLOCK to the cpu_get_real_ticks usages instead of it's implementation?

Only to the cpu_get_ticks usage.  The others are okay.

>>> +/*! Reads next clock value from the file.
>>> +    If clock kind read from the file is different from the parameter,
>>> +    the value is not used.
>>> +    If the parameter is -1, the clock value is read to the cache anyway. */
>>
>> In what case could the clock kind not match?
>>
> 
> It was used in full version which had to skip clock from the log while loading the VM state.

So can it be removed for now?

Paolo

>>
>>> +void replay_read_next_clock(unsigned int kind);
>>> +
>>>  /* Asynchronous events queue */
>>>
> 
> 
> Pavel Dovgalyuk
>