aboutsummaryrefslogtreecommitdiff
path: root/cpus.c
diff options
context:
space:
mode:
authorAlex Bennée <alex.bennee@linaro.org>2017-02-23 18:29:09 +0000
committerAlex Bennée <alex.bennee@linaro.org>2017-02-24 10:32:45 +0000
commit6546706d28bbcec5c14601b446c0a1cde5256597 (patch)
treee5297c60dbd9958bb6a5d8223995f689fb5a74cb /cpus.c
parent8d4e9146b3568022ea5730d92841345d41275d66 (diff)
downloadqemu-6546706d28bbcec5c14601b446c0a1cde5256597.zip
qemu-6546706d28bbcec5c14601b446c0a1cde5256597.tar.gz
qemu-6546706d28bbcec5c14601b446c0a1cde5256597.tar.bz2
tcg: add kick timer for single-threaded vCPU emulation
Currently we rely on the side effect of the main loop grabbing the iothread_mutex to give any long running basic block chains a kick to ensure the next vCPU is scheduled. As this code is being re-factored and rationalised we now do it explicitly here. Signed-off-by: Alex Bennée <alex.bennee@linaro.org> Reviewed-by: Richard Henderson <rth@twiddle.net> Reviewed-by: Pranith Kumar <bobby.prani@gmail.com>
Diffstat (limited to 'cpus.c')
-rw-r--r--cpus.c61
1 files changed, 61 insertions, 0 deletions
diff --git a/cpus.c b/cpus.c
index c94b330..9fe56c9 100644
--- a/cpus.c
+++ b/cpus.c
@@ -768,6 +768,53 @@ void configure_icount(QemuOpts *opts, Error **errp)
}
/***********************************************************/
+/* TCG vCPU kick timer
+ *
+ * The kick timer is responsible for moving single threaded vCPU
+ * emulation on to the next vCPU. If more than one vCPU is running a
+ * timer event with force a cpu->exit so the next vCPU can get
+ * scheduled.
+ *
+ * The timer is removed if all vCPUs are idle and restarted again once
+ * idleness is complete.
+ */
+
+static QEMUTimer *tcg_kick_vcpu_timer;
+
+static void qemu_cpu_kick_no_halt(void);
+
+#define TCG_KICK_PERIOD (NANOSECONDS_PER_SECOND / 10)
+
+static inline int64_t qemu_tcg_next_kick(void)
+{
+ return qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL) + TCG_KICK_PERIOD;
+}
+
+static void kick_tcg_thread(void *opaque)
+{
+ timer_mod(tcg_kick_vcpu_timer, qemu_tcg_next_kick());
+ qemu_cpu_kick_no_halt();
+}
+
+static void start_tcg_kick_timer(void)
+{
+ if (!tcg_kick_vcpu_timer && CPU_NEXT(first_cpu)) {
+ tcg_kick_vcpu_timer = timer_new_ns(QEMU_CLOCK_VIRTUAL,
+ kick_tcg_thread, NULL);
+ timer_mod(tcg_kick_vcpu_timer, qemu_tcg_next_kick());
+ }
+}
+
+static void stop_tcg_kick_timer(void)
+{
+ if (tcg_kick_vcpu_timer) {
+ timer_del(tcg_kick_vcpu_timer);
+ tcg_kick_vcpu_timer = NULL;
+ }
+}
+
+
+/***********************************************************/
void hw_error(const char *fmt, ...)
{
va_list ap;
@@ -1021,9 +1068,12 @@ static void qemu_wait_io_event_common(CPUState *cpu)
static void qemu_tcg_wait_io_event(CPUState *cpu)
{
while (all_cpu_threads_idle()) {
+ stop_tcg_kick_timer();
qemu_cond_wait(cpu->halt_cond, &qemu_global_mutex);
}
+ start_tcg_kick_timer();
+
while (iothread_requesting_mutex) {
qemu_cond_wait(&qemu_io_proceeded_cond, &qemu_global_mutex);
}
@@ -1223,6 +1273,15 @@ static void deal_with_unplugged_cpus(void)
}
}
+/* Single-threaded TCG
+ *
+ * In the single-threaded case each vCPU is simulated in turn. If
+ * there is more than a single vCPU we create a simple timer to kick
+ * the vCPU and ensure we don't get stuck in a tight loop in one vCPU.
+ * This is done explicitly rather than relying on side-effects
+ * elsewhere.
+ */
+
static void *qemu_tcg_cpu_thread_fn(void *arg)
{
CPUState *cpu = arg;
@@ -1249,6 +1308,8 @@ static void *qemu_tcg_cpu_thread_fn(void *arg)
}
}
+ start_tcg_kick_timer();
+
/* process any pending work */
atomic_mb_set(&exit_request, 1);