Peter Crosthwaite <peter.crosthwa...@xilinx.com> writes:
> Modify Anthony's starvation detection logic to keep the BQL unlocked
> until the starvation condition goes away. Otherwise the counter has to
> count up to 1000 for each needed iteration until the busy-wait is
> lifted.
>
> Reset the counter back to zero once glib_pollfds_fill returns with a
> non-zero timout, (indicating a return to normality). The 1000 iteration
> wait now only happens once on the transition from normal operation to
> busy-wait starvation.
>
> Anthony's original patch fixed the serial paste bug, but this patch is
> also needed to restore performance.
>
> Signed-off-by: Peter Crosthwaite <peter.crosthwa...@xilinx.com>
I'm going through patches for 1.5 candidates.
I believe the paste performance issue has been resolved now and this
patch is no longer needed. I can't find a definitive statement on the
list for that though.
Peter, can you confirm?
Regards,
Anthony Liguori
> ---
> main-loop.c | 20 ++++++++++----------
> 1 files changed, 10 insertions(+), 10 deletions(-)
>
> diff --git a/main-loop.c b/main-loop.c
> index f46aece..93d2917 100644
> --- a/main-loop.c
> +++ b/main-loop.c
> @@ -200,10 +200,13 @@ static int os_host_main_loop_wait(uint32_t timeout)
> /* If the I/O thread is very busy or we are incorrectly busy waiting in
> * the I/O thread, this can lead to starvation of the BQL such that the
> * VCPU threads never run. To make sure we can detect the later case,
> - * print a message to the screen. If we run into this condition, create
> - * a fake timeout in order to give the VCPU threads a chance to run.
> + * print a message to the screen. If we run into this condition, unlock
> + * the BQL until a non-zero timout is given (indicating the starvation
> + * issue has gome away).
> */
> - if (spin_counter > MAX_MAIN_LOOP_SPIN) {
> + if (timeout > 0) {
> + spin_counter = 0;
> + } else if (spin_counter > MAX_MAIN_LOOP_SPIN) {
> static bool notified;
>
> if (!notified) {
> @@ -212,21 +215,18 @@ static int os_host_main_loop_wait(uint32_t timeout)
> MAX_MAIN_LOOP_SPIN);
> notified = true;
> }
> -
> - timeout = 1;
> }
>
> - if (timeout > 0) {
> - spin_counter = 0;
> + if (timeout > 0 || spin_counter > MAX_MAIN_LOOP_SPIN) {
> qemu_mutex_unlock_iothread();
> - } else {
> - spin_counter++;
> }
>
> ret = g_poll((GPollFD *)gpollfds->data, gpollfds->len, timeout);
>
> - if (timeout > 0) {
> + if (timeout > 0 || spin_counter > MAX_MAIN_LOOP_SPIN) {
> qemu_mutex_lock_iothread();
> + } else {
> + spin_counter++;
> }
>
> glib_pollfds_poll();
> --
> 1.7.0.4
