Message ID | 1434646046-27150-2-git-send-email-pbonzini@redhat.com |
---|---|
State | New |
Headers | show |
On 18/06/2015 18:47, 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! Hopefully :), this means dropping the iothread mutex as soon as possible and removing the iothread_requesting_mutex I guess.. Fred > > Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> > --- > cpus.c | 13 ++++++++----- > 1 file changed, 8 insertions(+), 5 deletions(-) > > diff --git a/cpus.c b/cpus.c > index de6469f..2e807f9 100644 > --- a/cpus.c > +++ b/cpus.c > @@ -924,7 +924,7 @@ 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; > @@ -1004,10 +1004,10 @@ 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; > @@ -1118,7 +1118,11 @@ 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) { > qemu_mutex_lock(&qemu_global_mutex); > atomic_dec(&iothread_requesting_mutex); > } else {
On 23/06/2015 15:49, Frederic Konrad wrote: >> >> Hopefully, multithreaded TCG will get rid of the whole logic to kick >> VCPUs whenever an I/O event occurs! > Hopefully :), this means dropping the iothread mutex as soon as possible > and removing the iothread_requesting_mutex I guess.. Yes---running most of cpu_exec outside the BQL, like KVM. io_read and io_write would have to get and release the lock if necessary. cpu_resume_from_signal also might have to release the lock. Paolo
On 23/06/2015 15:56, Paolo Bonzini wrote: > > On 23/06/2015 15:49, Frederic Konrad wrote: >>> Hopefully, multithreaded TCG will get rid of the whole logic to kick >>> VCPUs whenever an I/O event occurs! >> Hopefully :), this means dropping the iothread mutex as soon as possible >> and removing the iothread_requesting_mutex I guess.. > Yes---running most of cpu_exec outside the BQL, like KVM. io_read and > io_write would have to get and release the lock if necessary. > > cpu_resume_from_signal also might have to release the lock. > > Paolo Ok good, Can you add me in CC to this series so I can see when it's pulled etc please. Thanks, Fred
diff --git a/cpus.c b/cpus.c index de6469f..2e807f9 100644 --- a/cpus.c +++ b/cpus.c @@ -924,7 +924,7 @@ 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; @@ -1004,10 +1004,10 @@ 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; @@ -1118,7 +1118,11 @@ 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) { qemu_mutex_lock(&qemu_global_mutex); atomic_dec(&iothread_requesting_mutex);
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! Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> --- cpus.c | 13 ++++++++----- 1 file changed, 8 insertions(+), 5 deletions(-) } else {