Il 28/10/2013 17:32, Paolo Bonzini ha scritto:
> Stop/cont commands are broken with -icount due to a deadlock. The
> real problem is that the computation of timers_state.cpu_ticks_offset
> makes no sense with -icount enabled: we set it to an icount clock value
> in cpu_disable_ticks, and subtract a TSC (or similar, whatever
> cpu_get_real_ticks happens to return) value in cpu_enable_ticks.
>
> The fix is simple. timers_state.cpu_ticks_offset is only used
> together with cpu_get_real_ticks, so we can use cpu_get_real_ticks
> in cpu_disable_ticks. There is no need to update cpu_ticks_prev
> at the time cpu_disable_ticks is called; instead, we can do it
> the next time cpu_get_ticks is called.
>
> The change to cpu_disable_ticks is the important part of the patch.
> The rest modifies the code to always check timers_state.cpu_ticks_prev,
> even when the ticks are not advancing (i.e. the VM is stopped). It also
> makes a similar change to cpu_get_clock_locked, so that the code remains
> similar for cpu_get_ticks and cpu_get_clock_locked.
>
> Signed-off-by: Paolo Bonzini
> ---
> cpus.c | 42 ++
> 1 file changed, 22 insertions(+), 20 deletions(-)
>
> diff --git a/cpus.c b/cpus.c
> index 398229e..c2c6864 100644
> --- a/cpus.c
> +++ b/cpus.c
> @@ -165,36 +165,38 @@ int64_t cpu_get_icount(void)
> /* Caller must hold the BQL */
> int64_t cpu_get_ticks(void)
> {
> +int64_t ticks;
> +
> if (use_icount) {
> return cpu_get_icount();
> }
> -if (!timers_state.cpu_ticks_enabled) {
> -return timers_state.cpu_ticks_offset;
> -} else {
> -int64_t ticks;
> -ticks = cpu_get_real_ticks();
> -if (timers_state.cpu_ticks_prev > ticks) {
> -/* Note: non increasing ticks may happen if the host uses
> - software suspend */
> -timers_state.cpu_ticks_offset += timers_state.cpu_ticks_prev -
> ticks;
> -}
> -timers_state.cpu_ticks_prev = ticks;
> -return ticks + timers_state.cpu_ticks_offset;
> +
> +ticks = timers_state.cpu_ticks_offset;
> +if (timers_state.cpu_ticks_enabled) {
> +ticks += cpu_get_real_ticks();
> +}
> +
> +if (timers_state.cpu_ticks_prev > ticks) {
> +/* Note: non increasing ticks may happen if the host uses
> + software suspend */
> +timers_state.cpu_ticks_offset += timers_state.cpu_ticks_prev - ticks;
> +ticks = timers_state.cpu_ticks_prev;
> }
> +
> +timers_state.cpu_ticks_prev = ticks;
> +return ticks;
> }
>
> static int64_t cpu_get_clock_locked(void)
> {
> -int64_t ti;
> +int64_t ticks;
>
> -if (!timers_state.cpu_ticks_enabled) {
> -ti = timers_state.cpu_clock_offset;
> -} else {
> -ti = get_clock();
> -ti += timers_state.cpu_clock_offset;
> +ticks = timers_state.cpu_clock_offset;
> +if (timers_state.cpu_ticks_enabled) {
> +ticks += get_clock();
> }
>
> -return ti;
> +return ticks;
> }
>
> /* return the host CPU monotonic timer and handle stop/restart */
> @@ -235,7 +237,7 @@ void cpu_disable_ticks(void)
> /* Here, the really thing protected by seqlock is cpu_clock_offset. */
> seqlock_write_lock(&timers_state.vm_clock_seqlock);
> if (timers_state.cpu_ticks_enabled) {
> -timers_state.cpu_ticks_offset = cpu_get_ticks();
> +timers_state.cpu_ticks_offset += cpu_get_real_ticks();
> timers_state.cpu_clock_offset = cpu_get_clock_locked();
> timers_state.cpu_ticks_enabled = 0;
> }
>
Ping, did you miss this one?
Paolo
