Hi, This is the current state of my fixes for icount based record and replay. It doesn't completely fix the problem (hence the RFC status) but improves it to the point that I have been able to record and replay the boot of a vexpress kernel.
The first 3 patches are helper scripts I've been using during my debugging. The first is the only real fix and the following 2 should probably be dropped from any pull request as they introduce new features rather than fix something. We then have another BQL fix for i386. I haven't had a chance to replicate myself so far but it looks perfectly sane to me. Finally the fixes for icount: cpus: remove icount handling from qemu_tcg_cpu_thread_fn Simple clean-up as we don't do icount for MTTCG cpus: check cpu->running in cpu_get_icount_raw() I'm not sure the race happens and once outside of cpu->running the icount counters should be zero. However it seems a sensible precaution. cpus: move icount preparation out of tcg_exec_cpu This is a little light re-factoring that stops the icount work getting in the way of the main bit of tcg_exec_cpu. It also removed some redundant assignment and replaced them with asserts for now. cpus: don't credit executed instructions before they have run This is the main one which ensures we never jump forward in time and cpu_get_icount_raw() remains consistent. replay: gracefully handle backward time events This is the most hand-wavey patch. It glosses over the disparity in time between the vCPU thread and the main-loop by jumping forward to the most current time value. However it is not really deterministic and runs into potential problems with sequencing of log events. I think a better fix would be to extend replay_lock() so all related log events are serialised and we don't end up with interleaved events from the vCPU thread and the main-loop. I think the cpus: patches should probably go into the next pull-request while we see if we can come up with a better final solution for fixing record/replay. However given how long this regression has run during the release candidate process I wanted to update everyone on the current status and get feedback ASAP. Cheers, Alex Bennée (9): scripts/qemugdb/mtree.py: fix up mtree dump scripts/qemu-gdb/timers.py: new helper to dump timer state scripts/replay-dump.py: replay log dumper target/i386/misc_helper: wrap BQL around another IRQ generator cpus: remove icount handling from qemu_tcg_cpu_thread_fn cpus: check cpu->running in cpu_get_icount_raw() cpus: move icount preparation out of tcg_exec_cpu cpus: don't credit executed instructions before they have run replay: gracefully handle backward time events cpus.c | 94 +++++++++++----- include/qom/cpu.h | 1 + replay/replay-internal.c | 7 ++ replay/replay.c | 9 +- scripts/qemu-gdb.py | 3 +- scripts/qemugdb/mtree.py | 12 +- scripts/qemugdb/timers.py | 54 +++++++++ scripts/replay-dump.py | 272 ++++++++++++++++++++++++++++++++++++++++++++++ target/i386/misc_helper.c | 3 + 9 files changed, 423 insertions(+), 32 deletions(-) create mode 100644 scripts/qemugdb/timers.py create mode 100755 scripts/replay-dump.py -- 2.11.0
