From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:54957) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Z7Jsn-0004jD-Lf for qemu-devel@nongnu.org; Tue, 23 Jun 2015 04:48:42 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Z7Jsm-0000ie-Ny for qemu-devel@nongnu.org; Tue, 23 Jun 2015 04:48:41 -0400 Received: from mx1.redhat.com ([209.132.183.28]:41541) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Z7Jsm-0000ia-Gk for qemu-devel@nongnu.org; Tue, 23 Jun 2015 04:48:40 -0400 Date: Tue, 23 Jun 2015 16:48:37 +0800 From: Fam Zheng Message-ID: <20150623084837.GA2028@ad.nay.redhat.com> References: <1434646046-27150-1-git-send-email-pbonzini@redhat.com> <1434646046-27150-3-git-send-email-pbonzini@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1434646046-27150-3-git-send-email-pbonzini@redhat.com> Subject: Re: [Qemu-devel] [PATCH 2/9] main-loop: introduce qemu_mutex_iothread_locked List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Paolo Bonzini Cc: jan.kiszka@siemens.com, qemu-devel@nongnu.org On Thu, 06/18 18:47, Paolo Bonzini wrote: > 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! > > Signed-off-by: Paolo Bonzini > --- > cpus.c | 9 +++++++++ > include/qemu/main-loop.h | 10 ++++++++++ > stubs/iothread-lock.c | 5 +++++ > 3 files changed, 24 insertions(+) > > diff --git a/cpus.c b/cpus.c > index 2e807f9..9531d03 100644 > --- a/cpus.c > +++ b/cpus.c > @@ -1116,6 +1116,13 @@ bool qemu_in_vcpu_thread(void) > return current_cpu && qemu_cpu_is_self(current_cpu); > } > > +static __thread bool iothread_locked = false; > + > +bool qemu_mutex_iothread_locked(void) > +{ > + return iothread_locked; > +} > + > void qemu_mutex_lock_iothread(void) > { > atomic_inc(&iothread_requesting_mutex); > @@ -1133,10 +1140,12 @@ void qemu_mutex_lock_iothread(void) > atomic_dec(&iothread_requesting_mutex); > qemu_cond_broadcast(&qemu_io_proceeded_cond); > } > + iothread_locked = true; > } > > void qemu_mutex_unlock_iothread(void) > { > + iothread_locked = false; > qemu_mutex_unlock(&qemu_global_mutex); > } > > diff --git a/include/qemu/main-loop.h b/include/qemu/main-loop.h > index 62c68c0..6b74eb9 100644 > --- a/include/qemu/main-loop.h > +++ b/include/qemu/main-loop.h > @@ -270,6 +270,16 @@ 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 > diff --git a/stubs/iothread-lock.c b/stubs/iothread-lock.c > index 5d8aca1..dda6f6b 100644 > --- a/stubs/iothread-lock.c > +++ b/stubs/iothread-lock.c > @@ -1,6 +1,11 @@ > #include "qemu-common.h" > #include "qemu/main-loop.h" > > +bool qemu_mutex_iothread_locked(void) > +{ > + return true; > +} > + > void qemu_mutex_lock_iothread(void) > { > } > -- > 1.8.3.1 > > > Reviewed-by: Fam Zheng