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system/qdev-monitor: move drain_call_rcu call under if (!dev) in qmp_device_add()

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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 7bed89958b 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-gavr@yandex-team.ru>
Message-ID: <20231103105602.90475-1-ds-gavr@yandex-team.ru>
Fixes: 7bed89958b ("device_core: use drain_call_rcu in in qmp_device_add", 2020-10-12)
Cc: qemu-stable@nongnu.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Dmitrii Gavrilov 2023-11-03 13:56:02 +03:00 • committed by Paolo Bonzini
parent 9876359990
commit 012b170173
1 changed files with 11 additions and 12 deletions
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23
system/qdev-monitor.c
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@ -858,19 +858,18 @@ void qmp_device_add(QDict *qdict, QObject **ret_data, Error **errp)
return; return;
} }
dev = qdev_device_add(opts, errp); 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) { 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); qemu_opts_del(opts);
return; return;
} }