tcg: drop global lock during TCG code execution

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>

1 files changed, 10 insertions, 0 deletions

diff --git a/qom/cpu.c b/qom/cpu.c
index ed87c50cea..58784bcbea 100644
--- a/qom/cpu.c
+++ b/qom/cpu.c
@@ -113,9 +113,19 @@ static void cpu_common_get_memory_mapping(CPUState *cpu,
     error_setg(errp, "Obtaining memory mappings is unsupported on this CPU.");
 }
 
+/* Resetting the IRQ comes from across the code base so we take the
+ * BQL here if we need to.  cpu_interrupt assumes it is held.*/
 void cpu_reset_interrupt(CPUState *cpu, int mask)
 {
+    bool need_lock = !qemu_mutex_iothread_locked();
+
+    if (need_lock) {
+        qemu_mutex_lock_iothread();
+    }
     cpu->interrupt_request &= ~mask;
+    if (need_lock) {
+        qemu_mutex_unlock_iothread();
+    }
 }
 
 void cpu_exit(CPUState *cpu)