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Re: [Qemu-devel] [RFC PATCH v4 07/25] icount: implement icount requestin
From: |
Pavel Dovgaluk |
Subject: |
Re: [Qemu-devel] [RFC PATCH v4 07/25] icount: implement icount requesting |
Date: |
Tue, 11 Nov 2014 12:41:40 +0300 |
> From: Frederic Konrad [mailto:address@hidden
> On 07/11/2014 12:36, Pavel Dovgaluk wrote:
> >> From: Paolo Bonzini [mailto:address@hidden
> >> On 07/11/2014 11:32, Pavel Dovgalyuk wrote:
> >>> Replay uses number of executed instructions to determine corrent events
> >>> injection moments. This patch introduces new function for querying the
> >>> instructions counter.
> >>>
> >>> Signed-off-by: Pavel Dovgalyuk <address@hidden>
> >>> ---
> >>> cpus.c | 26 +++++++++++++++++++++++---
> >>> include/qemu/timer.h | 1 +
> >>> 2 files changed, 24 insertions(+), 3 deletions(-)
> >>>
> >>> diff --git a/cpus.c b/cpus.c
> >>> index 7e8c507..2ec6d75 100644
> >>> --- a/cpus.c
> >>> +++ b/cpus.c
> >>> @@ -136,8 +136,7 @@ typedef struct TimersState {
> >>>
> >>> static TimersState timers_state;
> >>>
> >>> -/* Return the virtual CPU time, based on the instruction counter. */
> >>> -static int64_t cpu_get_icount_locked(void)
> >>> +static int64_t cpu_get_instructions_counter_locked(void)
> >>> {
> >>> int64_t icount;
> >>> CPUState *cpu = current_cpu;
> >>> @@ -145,10 +144,31 @@ static int64_t cpu_get_icount_locked(void)
> >>> icount = timers_state.qemu_icount;
> >>> if (cpu) {
> >>> if (!cpu_can_do_io(cpu)) {
> >>> - fprintf(stderr, "Bad clock read\n");
> >>> + fprintf(stderr, "Bad icount read\n");
> >>> + exit(1);
> >>> }
> >>> icount -= (cpu->icount_decr.u16.low + cpu->icount_extra);
> >>> }
> >>> + return icount;
> >>> +}
> >>> +
> >>> +int64_t cpu_get_instructions_counter(void)
> >>> +{
> >>> + /* This function calls are synchnonized to timer changes,
> >>> + calling cpu_get_instructions_counter_locked without lock is safe
> >>> */
> >>> + int64_t icount = timers_state.qemu_icount;
> >>> + CPUState *cpu = current_cpu;
> >>> +
> >>> + if (cpu) {
> >>> + icount -= (cpu->icount_decr.u16.low + cpu->icount_extra);
> >>> + }
> >>> + return icount;
> >>> +}
> >> This is the same as Frederic's QEMU_CLOCK_ICOUNT clock, right? Any
> >> reason why one is better than the other?
> > Not really. Frederic's QEMU_CLOCK_ICOUNT is measured in nanoseconds.
> > And this counter is measured in instructions.
> >
> So you transformed your implementation to use icount?
Right, new implementation uses icount.
> I guess you replay event's according to the current instruction?
> I implemented icount clock with the QEMUTimer API so a callback can be
> notified during the replay at the right instruction.
We cannot use timers, because there are synchronization events
(like exceptions, interrupts, timer reads) that control the execution
correctness.
> By the way do you have a git tree somewhere where I can get the patches?
No, there is no public repository. There are only the patches in the mail list.
Pavel Dovgalyuk
- [Qemu-devel] [RFC PATCH v4 05/25] replay: internal functions for replay log, (continued)
[Qemu-devel] [RFC PATCH v4 08/25] icount: improve enable/disable ticks, Pavel Dovgalyuk, 2014/11/07
[Qemu-devel] [RFC PATCH v4 09/25] replay: introduce icount event, Pavel Dovgalyuk, 2014/11/07
[Qemu-devel] [RFC PATCH v4 10/25] i386: do not cross the pages boundaries in replay mode, Pavel Dovgalyuk, 2014/11/07
[Qemu-devel] [RFC PATCH v4 11/25] cpu-exec: allow temporary disabling icount, Pavel Dovgalyuk, 2014/11/07