Re: [Qemu-arm] [PATCH v9 08/25] tcg: drop global lock during TCG code execution

[Peter Maydell]

On 1 February 2017 at 15:05, Alex Bennée <address@hidden> wrote:
> From: Jan Kiszka <address@hidden>
>
> 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 <address@hidden>
> Message-Id: <address@hidden>
> [FK: Rebase, fix qemu_devices_reset deadlock, rm address_space_* mutex]
> Signed-off-by: KONRAD Frederic <address@hidden>
> [EGC: fixed iothread lock for cpu-exec IRQ handling]
> Signed-off-by: Emilio G. Cota <address@hidden>
> [AJB: -smp single-threaded fix, clean commit msg, BQL fixes]
> Signed-off-by: Alex Bennée <address@hidden>
> Reviewed-by: Richard Henderson <address@hidden>
> Reviewed-by: Pranith Kumar <address@hidden>

target/arm changes:
Acked-by: Peter Maydell <address@hidden>

-- PMM