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Re: [Qemu-devel] [RFC v3 13/19] tcg: rename tcg_current_cpu to tcg_curre
From: |
Alex Bennée |
Subject: |
Re: [Qemu-devel] [RFC v3 13/19] tcg: rename tcg_current_cpu to tcg_current_rr_cpu |
Date: |
Tue, 07 Jun 2016 13:59:01 +0100 |
User-agent: |
mu4e 0.9.17; emacs 25.0.94.5 |
Alex Bennée <address@hidden> writes:
> ..and make the definition local to cpus. In preparation for MTTCG the
> concept of a global tcg_current_cpu will no longer make sense. However
> we still need to keep track of it in the single-threaded case to be able
> to exit quickly when required.
>
> qemu_cpu_kick_no_halt() moves and becomes qemu_cpu_kick_rr_cpu() to
> emphasise its use-case. qemu_cpu_kick now kicks the relevant cpu as
> well as qemu_kick_rr_cpu() which will become a no-op in MTTCG.
I detected a failure case that a -smp 2 guest doesn't cleanly shutdown
in RR mode. My command line:
running command: ['/home/alex/lsrc/qemu/qemu.git/arm-softmmu/qemu-system-arm',
'-machine', 'type=virt', '-display', 'none', '-smp', '1', '-m', '4096', '-cpu',
'cortex-a15', '-serial', 'telnet:127.0.0.1:4444', '-monitor', 'stdio',
'-netdev', 'user,id=unet,hostfwd=tcp::2222-:22', '-device',
'virtio-net-device,netdev=unet', '-drive',
'file=/home/alex/lsrc/qemu/images/jessie-arm32.qcow2,id=myblock,index=0,if=none',
'-device', 'virtio-blk-device,drive=myblock', '-append', 'console=ttyAMA0
systemd.unit=benchmark.service root=/dev/vda1', '-kernel',
'/home/alex/lsrc/qemu/images/aarch32-current-linux-kernel-only.img', '-smp',
'2'] (notty=False, with timeout)
command timed out!
run 1: ret=-1 (FALSE), time=20.000228 (0/1)
1 fails
(N.B. the duplicate -smp is just an artefact of my shell script glue.
The -smp 2 is the final smp that gets acted on. The benchmark.service is
just a simple systemd target that shuts the image down again.)
>
> Signed-off-by: Alex Bennée <address@hidden>
> ---
> cpu-exec-common.c | 1 -
> cpu-exec.c | 3 ---
> cpus.c | 41 ++++++++++++++++++++++++-----------------
> include/exec/exec-all.h | 2 --
> 4 files changed, 24 insertions(+), 23 deletions(-)
>
> diff --git a/cpu-exec-common.c b/cpu-exec-common.c
> index 132cd03..f42d24a 100644
> --- a/cpu-exec-common.c
> +++ b/cpu-exec-common.c
> @@ -24,7 +24,6 @@
> #include "exec/memory-internal.h"
>
> bool exit_request;
> -CPUState *tcg_current_cpu;
>
> /* exit the current TB from a signal handler. The host registers are
> restored in a state compatible with the CPU emulator
> diff --git a/cpu-exec.c b/cpu-exec.c
> index ae81e8e..68e804b 100644
> --- a/cpu-exec.c
> +++ b/cpu-exec.c
> @@ -597,7 +597,6 @@ int cpu_exec(CPUState *cpu)
> return EXCP_HALTED;
> }
>
> - atomic_mb_set(&tcg_current_cpu, cpu);
> rcu_read_lock();
>
> if (unlikely(atomic_mb_read(&exit_request))) {
> @@ -658,7 +657,5 @@ int cpu_exec(CPUState *cpu)
> /* fail safe : never use current_cpu outside cpu_exec() */
> current_cpu = NULL;
>
> - /* Does not need atomic_mb_set because a spurious wakeup is okay. */
> - atomic_set(&tcg_current_cpu, NULL);
> return ret;
> }
> diff --git a/cpus.c b/cpus.c
> index 12e04c9..a139ad3 100644
> --- a/cpus.c
> +++ b/cpus.c
> @@ -942,6 +942,7 @@ void run_on_cpu(CPUState *cpu, void (*func)(void *data),
> void *data)
> {
> struct qemu_work_item wi;
>
> + /* Always true when using tcg RR scheduling from a vCPU context */
> if (qemu_cpu_is_self(cpu)) {
> func(data);
> return;
> @@ -1216,15 +1217,29 @@ static int tcg_cpu_exec(CPUState *cpu)
> * This is done explicitly rather than relying on side-effects
> * elsewhere.
> */
> -static void qemu_cpu_kick_no_halt(void);
> #define TCG_KICK_FREQ (qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL) + \
> NANOSECONDS_PER_SECOND / 10)
>
> +/* only used in single-thread tcg mode */
> +static CPUState *tcg_current_rr_cpu;
> +
> +/* Kick the currently round-robin scheduled vCPU */
> +static void qemu_cpu_kick_rr_cpu(void)
> +{
> + CPUState *cpu;
> + do {
> + cpu = atomic_mb_read(&tcg_current_rr_cpu);
> + if (cpu) {
> + cpu_exit(cpu);
> + }
> + } while (cpu != atomic_mb_read(&tcg_current_rr_cpu));
> +}
> +
> static void kick_tcg_thread(void *opaque)
> {
> QEMUTimer *self = *(QEMUTimer **) opaque;
> timer_mod(self, TCG_KICK_FREQ);
> - qemu_cpu_kick_no_halt();
> + qemu_cpu_kick_rr_cpu();
> }
>
> static void *qemu_tcg_cpu_thread_fn(void *arg)
> @@ -1275,6 +1290,7 @@ static void *qemu_tcg_cpu_thread_fn(void *arg)
> }
>
> for (; cpu != NULL && !exit_request; cpu = CPU_NEXT(cpu)) {
> + atomic_mb_set(&tcg_current_rr_cpu, cpu);
>
> qemu_clock_enable(QEMU_CLOCK_VIRTUAL,
> (cpu->singlestep_enabled & SSTEP_NOTIMER) ==
> 0);
> @@ -1290,6 +1306,8 @@ static void *qemu_tcg_cpu_thread_fn(void *arg)
> }
>
> } /* for cpu.. */
> + /* Does not need atomic_mb_set because a spurious wakeup is okay. */
> + atomic_set(&tcg_current_rr_cpu, NULL);
>
> /* Pairs with smp_wmb in qemu_cpu_kick. */
> atomic_mb_set(&exit_request, 0);
> @@ -1326,24 +1344,13 @@ static void qemu_cpu_kick_thread(CPUState *cpu)
> #endif
> }
>
> -static void qemu_cpu_kick_no_halt(void)
> -{
> - CPUState *cpu;
> - /* Ensure whatever caused the exit has reached the CPU threads before
> - * writing exit_request.
> - */
> - atomic_mb_set(&exit_request, 1);
> - cpu = atomic_mb_read(&tcg_current_cpu);
> - if (cpu) {
> - cpu_exit(cpu);
> - }
> -}
> -
> void qemu_cpu_kick(CPUState *cpu)
> {
> qemu_cond_broadcast(cpu->halt_cond);
> if (tcg_enabled()) {
> - qemu_cpu_kick_no_halt();
> + cpu_exit(cpu);
> + /* Also ensure current RR cpu is kicked */
> + qemu_cpu_kick_rr_cpu();
> } else {
> qemu_cpu_kick_thread(cpu);
> }
> @@ -1384,7 +1391,7 @@ void qemu_mutex_lock_iothread(void)
> atomic_dec(&iothread_requesting_mutex);
> } else {
> if (qemu_mutex_trylock(&qemu_global_mutex)) {
> - qemu_cpu_kick_no_halt();
> + qemu_cpu_kick_rr_cpu();
> qemu_mutex_lock(&qemu_global_mutex);
> }
> atomic_dec(&iothread_requesting_mutex);
> diff --git a/include/exec/exec-all.h b/include/exec/exec-all.h
> index e30f02b..31f4c38 100644
> --- a/include/exec/exec-all.h
> +++ b/include/exec/exec-all.h
> @@ -405,8 +405,6 @@ bool memory_region_is_unassigned(MemoryRegion *mr);
> /* vl.c */
> extern int singlestep;
>
> -/* cpu-exec.c, accessed with atomic_mb_read/atomic_mb_set */
> -extern CPUState *tcg_current_cpu;
> extern bool exit_request;
>
> #endif
--
Alex Bennée
- Re: [Qemu-devel] [RFC v3 12/19] tcg: add kick timer for single-threaded vCPU emulation, (continued)
Re: [Qemu-devel] [RFC v3 13/19] tcg: rename tcg_current_cpu to tcg_current_rr_cpu,
Alex Bennée <=
[Qemu-devel] [RFC v3 14/19] tcg: remove global exit_request, Alex Bennée, 2016/06/03
[Qemu-devel] [RFC v3 09/19] target-arm/arm-powerctl: wake up sleeping CPUs, Alex Bennée, 2016/06/03
[Qemu-devel] [RFC v3 10/19] tcg: cpus rm tcg_exec_all(), Alex Bennée, 2016/06/03
[Qemu-devel] [RFC v3 18/19] tcg: Ensure safe TB lookup out of 'tb_lock', Alex Bennée, 2016/06/03
[Qemu-devel] [RFC v3 17/19] tcg: enable thread-per-vCPU, Alex Bennée, 2016/06/03
[Qemu-devel] [RFC v3 15/19] tcg: drop global lock during TCG code execution, Alex Bennée, 2016/06/03