On Fri, 3 Nov 2023 13:56:02 +0300 Dmitrii Gavrilov <ds-g...@yandex-team.ru> wrote:
Seems related to cpu hotpug issues, CCing Boris for awareness. > Original goal of addition of drain_call_rcu to qmp_device_add was to cover > the failure case of qdev_device_add. It seems call of drain_call_rcu was > misplaced in 7bed89958bfbf40df what led to waiting for pending RCU callbacks > under happy path too. What led to overall performance degradation of > qmp_device_add. > > In this patch call of drain_call_rcu moved under handling of failure of > qdev_device_add. > > Signed-off-by: Dmitrii Gavrilov <ds-g...@yandex-team.ru> > --- > system/qdev-monitor.c | 23 +++++++++++------------ > 1 file changed, 11 insertions(+), 12 deletions(-) > > diff --git a/system/qdev-monitor.c b/system/qdev-monitor.c > index 1b8005a..dc7b02d 100644 > --- a/system/qdev-monitor.c > +++ b/system/qdev-monitor.c > @@ -856,19 +856,18 @@ void qmp_device_add(QDict *qdict, QObject **ret_data, > Error **errp) > return; > } > dev = qdev_device_add(opts, errp); > - > - /* > - * Drain all pending RCU callbacks. This is done because > - * some bus related operations can delay a device removal > - * (in this case this can happen if device is added and then > - * removed due to a configuration error) > - * to a RCU callback, but user might expect that this interface > - * will finish its job completely once qmp command returns result > - * to the user > - */ > - drain_call_rcu(); > - > if (!dev) { > + /* > + * Drain all pending RCU callbacks. This is done because > + * some bus related operations can delay a device removal > + * (in this case this can happen if device is added and then > + * removed due to a configuration error) > + * to a RCU callback, but user might expect that this interface > + * will finish its job completely once qmp command returns result > + * to the user > + */ > + drain_call_rcu(); > + > qemu_opts_del(opts); > return; > }