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Re: [Qemu-devel] [RFC v2 07/11] linux-user: Rework exclusive operation m
From: |
Alex Bennée |
Subject: |
Re: [Qemu-devel] [RFC v2 07/11] linux-user: Rework exclusive operation mechanism |
Date: |
Thu, 14 Jul 2016 16:04:30 +0100 |
User-agent: |
mu4e 0.9.17; emacs 25.0.95.9 |
Sergey Fedorov <address@hidden> writes:
> From: Sergey Fedorov <address@hidden>
>
> A single variable 'pending_cpus' was used for both counting currently
> running CPUs and for signalling the pending exclusive operation request.
>
> To prepare for supporting operations which requires a quiescent state,
> like translation buffer flush, it is useful to keep a counter of
> currently running CPUs always up to date.
>
> Use a separate variable 'tcg_pending_threads' to count for currently
> running CPUs and a separate variable 'exclusive_pending' to indicate
> that there's an exclusive operation pending.
>
> Signed-off-by: Sergey Fedorov <address@hidden>
> Signed-off-by: Sergey Fedorov <address@hidden>
> ---
>
> Changes in v2:
> - Rename 'tcg_pending_cpus' to 'tcg_pending_threads'
Reviewed-by: Alex Bennée <address@hidden>
>
> ---
> linux-user/main.c | 24 ++++++++++++------------
> 1 file changed, 12 insertions(+), 12 deletions(-)
>
> diff --git a/linux-user/main.c b/linux-user/main.c
> index bdbda693cc5f..5ff0b20bad89 100644
> --- a/linux-user/main.c
> +++ b/linux-user/main.c
> @@ -112,7 +112,8 @@ static QemuMutex cpu_list_mutex;
> static QemuMutex exclusive_lock;
> static QemuCond exclusive_cond;
> static QemuCond exclusive_resume;
> -static int pending_cpus;
> +static bool exclusive_pending;
> +static int tcg_pending_threads;
>
> void qemu_init_cpu_loop(void)
> {
> @@ -142,7 +143,8 @@ void fork_end(int child)
> QTAILQ_REMOVE(&cpus, cpu, node);
> }
> }
> - pending_cpus = 0;
> + tcg_pending_threads = 0;
> + exclusive_pending = false;
> qemu_mutex_init(&exclusive_lock);
> qemu_mutex_init(&cpu_list_mutex);
> qemu_cond_init(&exclusive_cond);
> @@ -159,7 +161,7 @@ void fork_end(int child)
> must be held. */
> static inline void exclusive_idle(void)
> {
> - while (pending_cpus) {
> + while (exclusive_pending) {
> qemu_cond_wait(&exclusive_resume, &exclusive_lock);
> }
> }
> @@ -173,15 +175,14 @@ static inline void start_exclusive(void)
> qemu_mutex_lock(&exclusive_lock);
> exclusive_idle();
>
> - pending_cpus = 1;
> + exclusive_pending = true;
> /* Make all other cpus stop executing. */
> CPU_FOREACH(other_cpu) {
> if (other_cpu->running) {
> - pending_cpus++;
> cpu_exit(other_cpu);
> }
> }
> - if (pending_cpus > 1) {
> + while (tcg_pending_threads) {
> qemu_cond_wait(&exclusive_cond, &exclusive_lock);
> }
> }
> @@ -189,7 +190,7 @@ static inline void start_exclusive(void)
> /* Finish an exclusive operation. */
> static inline void __attribute__((unused)) end_exclusive(void)
> {
> - pending_cpus = 0;
> + exclusive_pending = false;
> qemu_cond_broadcast(&exclusive_resume);
> qemu_mutex_unlock(&exclusive_lock);
> }
> @@ -200,6 +201,7 @@ static inline void cpu_exec_start(CPUState *cpu)
> qemu_mutex_lock(&exclusive_lock);
> exclusive_idle();
> cpu->running = true;
> + tcg_pending_threads++;
> qemu_mutex_unlock(&exclusive_lock);
> }
>
> @@ -208,11 +210,9 @@ static inline void cpu_exec_end(CPUState *cpu)
> {
> qemu_mutex_lock(&exclusive_lock);
> cpu->running = false;
> - if (pending_cpus > 1) {
> - pending_cpus--;
> - if (pending_cpus == 1) {
> - qemu_cond_signal(&exclusive_cond);
> - }
> + tcg_pending_threads--;
> + if (!tcg_pending_threads) {
> + qemu_cond_signal(&exclusive_cond);
> }
> exclusive_idle();
> qemu_mutex_unlock(&exclusive_lock);
--
Alex Bennée
- [Qemu-devel] [RFC v2 02/11] cpus: pass CPUState to run_on_cpu helpers, (continued)
- [Qemu-devel] [RFC v2 04/11] cpus: Wrap mutex used to protect CPU work, Sergey Fedorov, 2016/07/06
- [Qemu-devel] [RFC v2 05/11] cpus: Rename flush_queued_work(), Sergey Fedorov, 2016/07/06
- [Qemu-devel] [RFC v2 07/11] linux-user: Rework exclusive operation mechanism, Sergey Fedorov, 2016/07/06
- Re: [Qemu-devel] [RFC v2 07/11] linux-user: Rework exclusive operation mechanism,
Alex Bennée <=
- [Qemu-devel] [RFC v2 06/11] linux-user: Use QemuMutex and QemuCond, Sergey Fedorov, 2016/07/06
- [Qemu-devel] [RFC v2 08/11] linux-user: Add qemu_cpu_is_self() and qemu_cpu_kick(), Sergey Fedorov, 2016/07/06
- [Qemu-devel] [RFC v2 10/11] cpu-exec-common: Introduce async_safe_run_on_cpu(), Sergey Fedorov, 2016/07/06
- [Qemu-devel] [RFC v2 11/11] tcg: Make tb_flush() thread safe, Sergey Fedorov, 2016/07/06