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main-loop: introduce qemu_mutex_iothread_locked

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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 <fred.konrad@greensocs.com>
Message-Id: <1434646046-27150-3-git-send-email-pbonzini@redhat.com>
Reviewed-by: Fam Zheng <famz@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Paolo Bonzini 2015-06-18 18:47:19 +02:00
parent 2e7f7a3c86
commit afbe70535f
3 changed files with 24 additions and 0 deletions
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10
include/qemu/main-loop.h
View file

@ -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.
*