From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:33404) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Z82Oj-0007wD-83 for qemu-devel@nongnu.org; Thu, 25 Jun 2015 04:20:38 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Z82Oe-0005yl-Fr for qemu-devel@nongnu.org; Thu, 25 Jun 2015 04:20:37 -0400 Received: from mx1.redhat.com ([209.132.183.28]:43653) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Z82Oe-0005ye-7p for qemu-devel@nongnu.org; Thu, 25 Jun 2015 04:20:32 -0400 Message-ID: <558BB9CB.4010407@redhat.com> Date: Thu, 25 Jun 2015 10:20:27 +0200 From: Paolo Bonzini MIME-Version: 1.0 References: <1435163110-2724-1-git-send-email-pbonzini@redhat.com> <1435163110-2724-2-git-send-email-pbonzini@redhat.com> <20150625033945.GG17695@ad.nay.redhat.com> In-Reply-To: <20150625033945.GG17695@ad.nay.redhat.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH 1/9] main-loop: use qemu_mutex_lock_iothread consistently List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Fam Zheng Cc: borntraeger@de.ibm.com, qemu-devel@nongnu.org, Frederic Konrad On 25/06/2015 05:39, Fam Zheng wrote: > On Wed, 06/24 18:25, Paolo Bonzini wrote: >> The next patch will require the BQL to be always taken with >> qemu_mutex_lock_iothread(), while right now this isn'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: <1434646046-27150-2-git-send-email-pbonzini@redhat.com> > > Why is this "Message-Id:" included in the commit message if it's not final? > >> Signed-off-by: Paolo Bonzini >> --- >> cpus.c | 10 +++++++--- >> 1 file changed, 7 insertions(+), 3 deletions(-) >> >> diff --git a/cpus.c b/cpus.c >> index b85fb5f..02cca5d 100644 >> --- a/cpus.c >> +++ b/cpus.c >> @@ -953,7 +953,7 @@ static void *qemu_kvm_cpu_thread_fn(void *arg) >> CPUState *cpu = arg; >> int r; >> >> - qemu_mutex_lock(&qemu_global_mutex); >> + qemu_mutex_lock_iothread(); >> qemu_thread_get_self(cpu->thread); >> cpu->thread_id = qemu_get_thread_id(); >> cpu->can_do_io = 1; >> @@ -1033,10 +1033,10 @@ static void *qemu_tcg_cpu_thread_fn(void *arg) >> { >> CPUState *cpu = arg; >> >> + qemu_mutex_lock_iothread(); >> qemu_tcg_init_cpu_signals(); >> qemu_thread_get_self(cpu->thread); >> >> - qemu_mutex_lock(&qemu_global_mutex); >> CPU_FOREACH(cpu) { >> cpu->thread_id = qemu_get_thread_id(); >> cpu->created = true; >> @@ -1148,7 +1148,11 @@ bool qemu_in_vcpu_thread(void) >> void qemu_mutex_lock_iothread(void) >> { >> atomic_inc(&iothread_requesting_mutex); >> - if (!tcg_enabled() || !first_cpu || !first_cpu->thread) { >> + /* In the simple case there is no need to bump the VCPU thread out of >> + * TCG code execution. >> + */ >> + if (!tcg_enabled() || qemu_in_vcpu_thread() || >> + !first_cpu || !first_cpu->thread) { > > This looks like a separate change from the above > "qemu_mutex_lock(&qemu_global_mutex)" conversion. Why do they belong to the > same patch? Previously, a VCPU thread would never call qemu_mutex_lock_iothread(). Now, it can. While the change is only necessary when a call is introduced with current_cpu != NULL (that's patch 5), it should be in this patch or before because this is the one that changes the invariant. I put it in the same because the patch is already very very smal. Paolo > Fam > >> qemu_mutex_lock(&qemu_global_mutex); >> atomic_dec(&iothread_requesting_mutex); >> } else { >> -- >> 1.8.3.1 >> >>