| Message ID | 20200805181303.7822-18-robert.foley@linaro.org |
|---|---|
| State | New |
| Headers | show |
| Series | accel/tcg: remove implied BQL from cpu_handle_interrupt/exception path | expand |
On Wed, 5 Aug 2020 14:12:59 -0400 Robert Foley <robert.foley@linaro.org> wrote: > This is part of a series of changes to remove the implied BQL > from the common code of cpu_handle_interrupt and > cpu_handle_exception. As part of removing the implied BQL > from the common code, we are pushing the BQL holding > down into the per-arch implementation functions of > do_interrupt and cpu_exec_interrupt. > > The purpose of this set of changes is to set the groundwork > so that an arch could move towards removing > the BQL from the cpu_handle_interrupt/exception paths. > > This approach was suggested by Paolo Bonzini. > For reference, here are two key posts in the discussion, explaining > the reasoning/benefits of this approach. > https://lists.gnu.org/archive/html/qemu-devel/2020-07/msg08731.html > https://lists.gnu.org/archive/html/qemu-devel/2020-08/msg00044.html > > Signed-off-by: Robert Foley <robert.foley@linaro.org> > --- > target/s390x/excp_helper.c | 12 +++++++++++- > 1 file changed, 11 insertions(+), 1 deletion(-) > > diff --git a/target/s390x/excp_helper.c b/target/s390x/excp_helper.c > index dde7afc2f0..b215b4a4a7 100644 > --- a/target/s390x/excp_helper.c > +++ b/target/s390x/excp_helper.c > @@ -470,7 +470,10 @@ void s390_cpu_do_interrupt(CPUState *cs) > S390CPU *cpu = S390_CPU(cs); > CPUS390XState *env = &cpu->env; > bool stopped = false; > - > + bool bql = !qemu_mutex_iothread_locked(); > + if (bql) { > + qemu_mutex_lock_iothread(); > + } I'm not sure I like that conditional locking. Can we instead create __s390_cpu_do_interrupt() or so, move the meat of this function there, take the bql unconditionally here, and... > qemu_log_mask(CPU_LOG_INT, "%s: %d at psw=%" PRIx64 ":%" PRIx64 "\n", > __func__, cs->exception_index, env->psw.mask, env->psw.addr); > > @@ -541,10 +544,14 @@ try_deliver: > /* unhalt if we had a WAIT PSW somehwere in our injection chain */ > s390_cpu_unhalt(cpu); > } > + if (bql) { > + qemu_mutex_unlock_iothread(); > + } > } > > bool s390_cpu_exec_interrupt(CPUState *cs, int interrupt_request) > { > + qemu_mutex_lock_iothread(); > if (interrupt_request & CPU_INTERRUPT_HARD) { > S390CPU *cpu = S390_CPU(cs); > CPUS390XState *env = &cpu->env; > @@ -552,10 +559,12 @@ bool s390_cpu_exec_interrupt(CPUState *cs, int interrupt_request) > if (env->ex_value) { > /* Execution of the target insn is indivisible from > the parent EXECUTE insn. */ > + qemu_mutex_unlock_iothread(); > return false; > } > if (s390_cpu_has_int(cpu)) { > s390_cpu_do_interrupt(cs); ...call __s390_cpu_do_interrupt() here? > + qemu_mutex_unlock_iothread(); > return true; > } > if (env->psw.mask & PSW_MASK_WAIT) { > @@ -564,6 +573,7 @@ bool s390_cpu_exec_interrupt(CPUState *cs, int interrupt_request) > cpu_interrupt(CPU(cpu), CPU_INTERRUPT_HALT); > } > } > + qemu_mutex_unlock_iothread(); > return false; > } >
On 06/08/20 10:59, Cornelia Huck wrote: >> bool stopped = false; >> - >> + bool bql = !qemu_mutex_iothread_locked(); >> + if (bql) { >> + qemu_mutex_lock_iothread(); >> + } > I'm not sure I like that conditional locking. Can we instead create > __s390_cpu_do_interrupt() or so, move the meat of this function there, > take the bql unconditionally here, and... > Agreed, except the usual convention would be s390_cpu_do_interrupt_locked. Paolo
Paolo Bonzini <pbonzini@redhat.com> writes: > On 06/08/20 10:59, Cornelia Huck wrote: >>> bool stopped = false; >>> - >>> + bool bql = !qemu_mutex_iothread_locked(); >>> + if (bql) { >>> + qemu_mutex_lock_iothread(); >>> + } >> I'm not sure I like that conditional locking. Can we instead create >> __s390_cpu_do_interrupt() or so, move the meat of this function there, >> take the bql unconditionally here, and... >> > > Agreed, except the usual convention would be > s390_cpu_do_interrupt_locked. We should probably document this convention in CODING_STYLE.rst/Naming > > Paolo
diff --git a/target/s390x/excp_helper.c b/target/s390x/excp_helper.c index dde7afc2f0..b215b4a4a7 100644 --- a/target/s390x/excp_helper.c +++ b/target/s390x/excp_helper.c @@ -470,7 +470,10 @@ void s390_cpu_do_interrupt(CPUState *cs) S390CPU *cpu = S390_CPU(cs); CPUS390XState *env = &cpu->env; bool stopped = false; - + bool bql = !qemu_mutex_iothread_locked(); + if (bql) { + qemu_mutex_lock_iothread(); + } qemu_log_mask(CPU_LOG_INT, "%s: %d at psw=%" PRIx64 ":%" PRIx64 "\n", __func__, cs->exception_index, env->psw.mask, env->psw.addr); @@ -541,10 +544,14 @@ try_deliver: /* unhalt if we had a WAIT PSW somehwere in our injection chain */ s390_cpu_unhalt(cpu); } + if (bql) { + qemu_mutex_unlock_iothread(); + } } bool s390_cpu_exec_interrupt(CPUState *cs, int interrupt_request) { + qemu_mutex_lock_iothread(); if (interrupt_request & CPU_INTERRUPT_HARD) { S390CPU *cpu = S390_CPU(cs); CPUS390XState *env = &cpu->env; @@ -552,10 +559,12 @@ bool s390_cpu_exec_interrupt(CPUState *cs, int interrupt_request) if (env->ex_value) { /* Execution of the target insn is indivisible from the parent EXECUTE insn. */ + qemu_mutex_unlock_iothread(); return false; } if (s390_cpu_has_int(cpu)) { s390_cpu_do_interrupt(cs); + qemu_mutex_unlock_iothread(); return true; } if (env->psw.mask & PSW_MASK_WAIT) { @@ -564,6 +573,7 @@ bool s390_cpu_exec_interrupt(CPUState *cs, int interrupt_request) cpu_interrupt(CPU(cpu), CPU_INTERRUPT_HALT); } } + qemu_mutex_unlock_iothread(); return false; }
This is part of a series of changes to remove the implied BQL from the common code of cpu_handle_interrupt and cpu_handle_exception. As part of removing the implied BQL from the common code, we are pushing the BQL holding down into the per-arch implementation functions of do_interrupt and cpu_exec_interrupt. The purpose of this set of changes is to set the groundwork so that an arch could move towards removing the BQL from the cpu_handle_interrupt/exception paths. This approach was suggested by Paolo Bonzini. For reference, here are two key posts in the discussion, explaining the reasoning/benefits of this approach. https://lists.gnu.org/archive/html/qemu-devel/2020-07/msg08731.html https://lists.gnu.org/archive/html/qemu-devel/2020-08/msg00044.html Signed-off-by: Robert Foley <robert.foley@linaro.org> --- target/s390x/excp_helper.c | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-)