| Message ID | 161700514781.1141125.8890164582302771524.stgit@pasha-ThinkPad-X280 (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | replay: don't wait in run_on_cpu | expand |
On 29/03/21 10:05, Pavel Dovgalyuk wrote: > @@ -136,7 +137,13 @@ void do_run_on_cpu(CPUState *cpu, run_on_cpu_func func, run_on_cpu_data data, > { > struct qemu_work_item wi; > > - if (qemu_cpu_is_self(cpu)) { > + if (qemu_cpu_is_self(cpu) > + /* > + * vCPU thread is waiting when replay mutex is locked > + * and the task is not exclusive, the function may be called > + * without other synchronization. > + */ > + || (replay_mode != REPLAY_MODE_NONE && replay_mutex_locked())) { > func(cpu, data); > return; > } Is the "or" saying that the execution is using the lockstep mode? If so, can you put it in a separate function so that it's more self-explanatory and check if it should be used elsewhere? Thanks, Paolo
On 29.03.2021 12:42, Paolo Bonzini wrote: > On 29/03/21 10:05, Pavel Dovgalyuk wrote: >> @@ -136,7 +137,13 @@ void do_run_on_cpu(CPUState *cpu, run_on_cpu_func >> func, run_on_cpu_data data, >> { >> struct qemu_work_item wi; >> - if (qemu_cpu_is_self(cpu)) { >> + if (qemu_cpu_is_self(cpu) >> + /* >> + * vCPU thread is waiting when replay mutex is locked >> + * and the task is not exclusive, the function may be called >> + * without other synchronization. >> + */ >> + || (replay_mode != REPLAY_MODE_NONE && replay_mutex_locked())) { >> func(cpu, data); >> return; >> } > > Is the "or" saying that the execution is using the lockstep mode? If > so, can you put it in a separate function so that it's more > self-explanatory and check if it should be used elsewhere? It was replay (is that lockstep that you mentioned?). I check that the mutex is already locked, which means, that vCPU does nothing at this moment. Pavel Dovgalyuk
On 29/03/21 12:55, Pavel Dovgalyuk wrote: >>> >> >> Is the "or" saying that the execution is using the lockstep mode? If >> so, can you put it in a separate function so that it's more >> self-explanatory and check if it should be used elsewhere? > > It was replay (is that lockstep that you mentioned?). Lockstep in the sense that (as is the case in record/replay mode) the I/O thread and vCPU thread execute in turns. Paolo > I check that the mutex is already locked, which means, that vCPU > does nothing at this moment.
diff --git a/cpus-common.c b/cpus-common.c index 6e73d3e58d..38ff510175 100644 --- a/cpus-common.c +++ b/cpus-common.c @@ -23,6 +23,7 @@ #include "hw/core/cpu.h" #include "sysemu/cpus.h" #include "qemu/lockable.h" +#include "sysemu/replay.h" static QemuMutex qemu_cpu_list_lock; static QemuCond exclusive_cond; @@ -136,7 +137,13 @@ void do_run_on_cpu(CPUState *cpu, run_on_cpu_func func, run_on_cpu_data data, { struct qemu_work_item wi; - if (qemu_cpu_is_self(cpu)) { + if (qemu_cpu_is_self(cpu) + /* + * vCPU thread is waiting when replay mutex is locked + * and the task is not exclusive, the function may be called + * without other synchronization. + */ + || (replay_mode != REPLAY_MODE_NONE && replay_mutex_locked())) { func(cpu, data); return; } diff --git a/include/sysemu/replay.h b/include/sysemu/replay.h index 0f3b0f7eac..032256533b 100644 --- a/include/sysemu/replay.h +++ b/include/sysemu/replay.h @@ -62,6 +62,7 @@ extern char *replay_snapshot; void replay_mutex_lock(void); void replay_mutex_unlock(void); +bool replay_mutex_locked(void); /* Replay process control functions */ diff --git a/replay/replay-internal.h b/replay/replay-internal.h index 97649ed8d7..dada623527 100644 --- a/replay/replay-internal.h +++ b/replay/replay-internal.h @@ -117,7 +117,6 @@ void replay_get_array_alloc(uint8_t **buf, size_t *size); * synchronisation between vCPU and main-loop threads. */ void replay_mutex_init(void); -bool replay_mutex_locked(void); /*! Checks error status of the file. */ void replay_check_error(void); diff --git a/stubs/replay-tools.c b/stubs/replay-tools.c index 43296b3d4e..a42f2483d5 100644 --- a/stubs/replay-tools.c +++ b/stubs/replay-tools.c @@ -48,6 +48,11 @@ void replay_mutex_unlock(void) { } +bool replay_mutex_locked(void) +{ + return false; +} + void replay_register_char_driver(Chardev *chr) { }
In record/replay mode waiting for vCPU to execute the task scheduled by run_on_cpu may lead to deadlock, because when run_on_cpu is executed in main_loop (e.g., in loadvm processing) it holds replay mutex. This patch allows running scheduled task in iothread when it holds the replay mutex. Signed-off-by: Pavel Dovgalyuk <Pavel.Dovgalyuk@ispras.ru> --- cpus-common.c | 9 ++++++++- include/sysemu/replay.h | 1 + replay/replay-internal.h | 1 - stubs/replay-tools.c | 5 +++++ 4 files changed, 14 insertions(+), 2 deletions(-)