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authorPaolo Bonzini <pbonzini@redhat.com>2015-06-18 18:47:19 +0200
committerPaolo Bonzini <pbonzini@redhat.com>2015-07-01 15:45:50 +0200
commitafbe70535ff1a8a7a32910cc15ebecc0ba92e7da (patch)
tree1e12a91857ba9ce038e7c1c05fd901add373b36b /include/qemu
parent2e7f7a3c86f884a77296a137b7c730a4d580c5c9 (diff)
downloadhqemu-afbe70535ff1a8a7a32910cc15ebecc0ba92e7da.zip
hqemu-afbe70535ff1a8a7a32910cc15ebecc0ba92e7da.tar.gz
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 <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>
Diffstat (limited to 'include/qemu')
-rw-r--r--include/qemu/main-loop.h10
1 files changed, 10 insertions, 0 deletions
diff --git a/include/qemu/main-loop.h b/include/qemu/main-loop.h
index 0f4a0fd..bc18ca3 100644
--- a/include/qemu/main-loop.h
+++ b/include/qemu/main-loop.h
@@ -223,6 +223,16 @@ 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.
*
* This function locks the main loop mutex. The mutex is taken by
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