From afbe70535ff1a8a7a32910cc15ebecc0ba92e7da Mon Sep 17 00:00:00 2001 From: Paolo Bonzini Date: Thu, 18 Jun 2015 18:47:19 +0200 Subject: main-loop: introduce qemu_mutex_iothread_locked This function will be used to avoid recursive locking of the iothread lock whenever address_space_rw/ld*/st* are called with the BQL held, which is almost always the case. Tracking whether the iothread is owned is very cheap (just use a TLS variable) but requires some care because now the lock must always be taken with qemu_mutex_lock_iothread(). Previously this wasn't the case. Outside TCG mode this is not a problem. In TCG mode, we need to be careful and avoid the "prod out of compiled code" step if already in a VCPU thread. This is easily done with a check on current_cpu, i.e. qemu_in_vcpu_thread(). Hopefully, multithreaded TCG will get rid of the whole logic to kick VCPUs whenever an I/O event occurs! Cc: Frederic Konrad Message-Id: <1434646046-27150-3-git-send-email-pbonzini@redhat.com> Reviewed-by: Fam Zheng Signed-off-by: Paolo Bonzini --- include/qemu/main-loop.h | 10 ++++++++++ 1 file changed, 10 insertions(+) (limited to 'include/qemu/main-loop.h') diff --git a/include/qemu/main-loop.h b/include/qemu/main-loop.h index 0f4a0fd4b2..bc18ca30e4 100644 --- a/include/qemu/main-loop.h +++ b/include/qemu/main-loop.h @@ -222,6 +222,16 @@ void qemu_set_fd_handler(int fd, int qemu_add_child_watch(pid_t pid); #endif +/** + * qemu_mutex_iothread_locked: Return lock status of the main loop mutex. + * + * The main loop mutex is the coarsest lock in QEMU, and as such it + * must always be taken outside other locks. This function helps + * functions take different paths depending on whether the current + * thread is running within the main loop mutex. + */ +bool qemu_mutex_iothread_locked(void); + /** * qemu_mutex_lock_iothread: Lock the main loop mutex. * -- cgit 1.4.1