motorhead/qemu
1
0
Fork 0
mirror of https://github.com/Motorhead1991/qemu.git synced 2025-08-04 08:13:54 -06:00
Code Issues Projects Releases Packages Wiki Activity Actions

tcg: drop global lock during TCG code execution

Browse source 
This finally allows TCG to benefit from the iothread introduction: Drop
the global mutex while running pure TCG CPU code. Reacquire the lock
when entering MMIO or PIO emulation, or when leaving the TCG loop.

We have to revert a few optimization for the current TCG threading
model, namely kicking the TCG thread in qemu_mutex_lock_iothread and not
kicking it in qemu_cpu_kick. We also need to disable RAM block
reordering until we have a more efficient locking mechanism at hand.

Still, a Linux x86 UP guest and my Musicpal ARM model boot fine here.
These numbers demonstrate where we gain something:

20338 jan       20   0  331m  75m 6904 R   99  0.9   0:50.95 qemu-system-arm
20337 jan       20   0  331m  75m 6904 S   20  0.9   0:26.50 qemu-system-arm

The guest CPU was fully loaded, but the iothread could still run mostly
independent on a second core. Without the patch we don't get beyond

32206 jan       20   0  330m  73m 7036 R   82  0.9   1:06.00 qemu-system-arm
32204 jan       20   0  330m  73m 7036 S   21  0.9   0:17.03 qemu-system-arm

We don't benefit significantly, though, when the guest is not fully
loading a host CPU.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Message-Id: <1439220437-23957-10-git-send-email-fred.konrad@greensocs.com>
[FK: Rebase, fix qemu_devices_reset deadlock, rm address_space_* mutex]
Signed-off-by: KONRAD Frederic <fred.konrad@greensocs.com>
[EGC: fixed iothread lock for cpu-exec IRQ handling]
Signed-off-by: Emilio G. Cota <cota@braap.org>
[AJB: -smp single-threaded fix, clean commit msg, BQL fixes]
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Richard Henderson <rth@twiddle.net>
Reviewed-by: Pranith Kumar <bobby.prani@gmail.com>
[PM: target-arm changes]
Acked-by: Peter Maydell <peter.maydell@linaro.org>
This commit is contained in:
Jan Kiszka 2017-02-23 18:29:11 +00:00 • committed by Alex Bennée
parent 791158d93b
commit 8d04fb55de
18 changed files with 166 additions and 49 deletions
Download patch file Download diff file Expand all files Collapse all files

28
cpus.c
View file

@ -1027,8 +1027,6 @@ static void qemu_kvm_init_cpu_signals(CPUState *cpu)
#endif /* _WIN32 */
static QemuMutex qemu_global_mutex;
static QemuCond qemu_io_proceeded_cond;
static unsigned iothread_requesting_mutex;
static QemuThread io_thread;
@ -1042,7 +1040,6 @@ void qemu_init_cpu_loop(void)
qemu_init_sigbus();
qemu_cond_init(&qemu_cpu_cond);
qemu_cond_init(&qemu_pause_cond);
qemu_cond_init(&qemu_io_proceeded_cond);
qemu_mutex_init(&qemu_global_mutex);
qemu_thread_get_self(&io_thread);
@ -1085,10 +1082,6 @@ static void qemu_tcg_wait_io_event(CPUState *cpu)
start_tcg_kick_timer();
while (iothread_requesting_mutex) {
qemu_cond_wait(&qemu_io_proceeded_cond, &qemu_global_mutex);
}
CPU_FOREACH(cpu) {
qemu_wait_io_event_common(cpu);
}
@ -1249,9 +1242,11 @@ static int tcg_cpu_exec(CPUState *cpu)
cpu->icount_decr.u16.low = decr;
cpu->icount_extra = count;
}
qemu_mutex_unlock_iothread();
cpu_exec_start(cpu);
ret = cpu_exec(cpu);
cpu_exec_end(cpu);
qemu_mutex_lock_iothread();
#ifdef CONFIG_PROFILER
tcg_time += profile_getclock() - ti;
#endif
@ -1479,27 +1474,14 @@ bool qemu_mutex_iothread_locked(void)
void qemu_mutex_lock_iothread(void)
{
atomic_inc(&iothread_requesting_mutex);
/* In the simple case there is no need to bump the VCPU thread out of
* TCG code execution.
*/
if (!tcg_enabled() || qemu_in_vcpu_thread() ||
!first_cpu || !first_cpu->created) {
qemu_mutex_lock(&qemu_global_mutex);
atomic_dec(&iothread_requesting_mutex);
} else {
if (qemu_mutex_trylock(&qemu_global_mutex)) {
qemu_cpu_kick_rr_cpu();
qemu_mutex_lock(&qemu_global_mutex);
}
atomic_dec(&iothread_requesting_mutex);
qemu_cond_broadcast(&qemu_io_proceeded_cond);
}
g_assert(!qemu_mutex_iothread_locked());
qemu_mutex_lock(&qemu_global_mutex);
iothread_locked = true;
}
void qemu_mutex_unlock_iothread(void)
{
g_assert(qemu_mutex_iothread_locked());
iothread_locked = false;
qemu_mutex_unlock(&qemu_global_mutex);
}