main-loop: introduce qemu_mutex_iothread_locked
commitafbe70535ff1a8a7a32910cc15ebecc0ba92e7da
authorPaolo Bonzini <pbonzini@redhat.com>
Thu, 18 Jun 2015 16:47:19 +0000 (18 18:47 +0200)
committerPaolo Bonzini <pbonzini@redhat.com>
Wed, 1 Jul 2015 13:45:50 +0000 (1 15:45 +0200)
tree1e12a91857ba9ce038e7c1c05fd901add373b36b
parent2e7f7a3c86f884a77296a137b7c730a4d580c5c9
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>
cpus.c
include/qemu/main-loop.h
stubs/iothread-lock.c