Re: [Qemu-devel] [RFC v1 09/11] tcg: drop global lock during TCG code execution

[Paolo Bonzini]

On 18/03/2016 17:18, Alex Bennée wrote:
> From: KONRAD Frederic <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.
> 
> Message-Id: <address@hidden>
> Signed-off-by: KONRAD Frederic <address@hidden>
> [AJB: -smp single-threaded fix, rm old info from commit msg]
> Signed-off-by: Alex Bennée <address@hidden>

You should probably squash this and patch 10 together.

Paolo