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

[Pavel Dovgaluk]

> From: Paolo Bonzini [mailto:address@hidden
> 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 <address@hidden>
> > ---
> >  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?

> 
> > +{
> > +    return REPLAY_CLOCK(REPLAY_CLOCK_REAL_TICKS, 
> > cpu_get_real_ticks_impl());
> > +}
> > +
> >  #ifdef CONFIG_PROFILER
> >  static inline int64_t profile_getclock(void)
> >  {
> > diff --git a/qemu-timer.c b/qemu-timer.c
> > index 98d9d1b..bc981a2 100644
> > --- a/qemu-timer.c
> > +++ b/qemu-timer.c
> > @@ -25,6 +25,7 @@
> >  #include "sysemu/sysemu.h"
> >  #include "monitor/monitor.h"
> >  #include "ui/console.h"
> > +#include "replay/replay.h"
> >
> >  #include "hw/hw.h"
> >
> > @@ -566,15 +567,15 @@ int64_t qemu_clock_get_ns(QEMUClockType type)
> >              return cpu_get_clock();
> >          }
> >      case QEMU_CLOCK_HOST:
> > -        now = get_clock_realtime();
> > +        now = REPLAY_CLOCK(REPLAY_CLOCK_HOST, get_clock_realtime());
> >          last = clock->last;
> >          clock->last = now;
> > -        if (now < last) {
> > +        if (now < last && replay_mode == REPLAY_MODE_NONE) {
> >              notifier_list_notify(&clock->reset_notifiers, &now);
> >          }
> >          return now;
> >      case QEMU_CLOCK_VIRTUAL_RT:
> > -        return cpu_get_clock();
> > +        return REPLAY_CLOCK(REPLAY_CLOCK_VIRTUAL_RT, cpu_get_clock());
> >      }
> >  }
> >
> > diff --git a/replay/Makefile.objs b/replay/Makefile.objs
> > index 56da09c..257c320 100755
> > --- a/replay/Makefile.objs
> > +++ b/replay/Makefile.objs
> > @@ -1,3 +1,4 @@
> >  obj-y += replay.o
> >  obj-y += replay-internal.o
> >  obj-y += replay-events.o
> > +obj-y += replay-time.o
> > diff --git a/replay/replay-internal.h b/replay/replay-internal.h
> > index 1666d6e..e906ec3 100755
> > --- a/replay/replay-internal.h
> > +++ b/replay/replay-internal.h
> > @@ -22,7 +22,10 @@ enum ReplayEvents {
> >      /* for emulated exceptions */
> >      EVENT_EXCEPTION,
> >      /* for async events */
> > -    EVENT_ASYNC
> > +    EVENT_ASYNC,
> > +    /* for clock read/writes */
> > +    /* some of grteater codes are reserved for clocks */
> > +    EVENT_CLOCK
> >  };
> >
> >  /* Asynchronous events IDs */
> > @@ -34,6 +37,8 @@ enum ReplayAsyncEventKind {
> >  typedef enum ReplayAsyncEventKind ReplayAsyncEventKind;
> >
> >  typedef struct ReplayState {
> > +    /*! Cached clock values. */
> > +    int64_t cached_clock[REPLAY_CLOCK_COUNT];
> >      /*! Current step - number of processed instructions and timer events. 
> > */
> >      uint64_t current_step;
> >      /*! Number of instructions to be executed before other events happen. 
> > */
> > @@ -88,6 +93,12 @@ bool skip_async_events(int stop_event);
> >      reports an error and stops the execution. */
> >  void skip_async_events_until(unsigned int kind);
> >
> > +/*! 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.

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


Pavel Dovgalyuk