| Message ID | 20181025144644.15464-30-cota@braap.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [RFC,v4,01/71] cpu: convert queued work to a QSIMPLEQ | expand |
On 10/25/18 3:46 PM, Emilio G. Cota wrote: > Add a comment about how atomic_read works here. The comment refers to > a "BQL-less CPU loop", which will materialize toward the end > of this series. > > Note that the modifications to cpu_reset_interrupt are there to > avoid deadlock during the CPU lock transition; once that is complete, > cpu_interrupt_request will be simple again. > > Signed-off-by: Emilio G. Cota <cota@braap.org> > --- > include/qom/cpu.h | 37 +++++++++++++++++++++++++++++++++++++ > qom/cpu.c | 27 +++++++++++++++++++++------ > 2 files changed, 58 insertions(+), 6 deletions(-) Reviewed-by: Richard Henderson <richard.henderson@linaro.org> r~
Emilio G. Cota <cota@braap.org> writes: > Add a comment about how atomic_read works here. The comment refers to > a "BQL-less CPU loop", which will materialize toward the end > of this series. > > Note that the modifications to cpu_reset_interrupt are there to > avoid deadlock during the CPU lock transition; once that is complete, > cpu_interrupt_request will be simple again. > <snip> > --- a/qom/cpu.c > +++ b/qom/cpu.c > @@ -98,14 +98,29 @@ static void cpu_common_get_memory_mapping(CPUState *cpu, > * BQL here if we need to. cpu_interrupt assumes it is held.*/ > void cpu_reset_interrupt(CPUState *cpu, int mask) > { > - bool need_lock = !qemu_mutex_iothread_locked(); > + bool has_bql = qemu_mutex_iothread_locked(); > + bool has_cpu_lock = cpu_mutex_locked(cpu); > > - if (need_lock) { > - qemu_mutex_lock_iothread(); > + if (has_bql) { > + if (has_cpu_lock) { > + atomic_set(&cpu->interrupt_request, cpu->interrupt_request & ~mask); > + } else { > + cpu_mutex_lock(cpu); > + atomic_set(&cpu->interrupt_request, cpu->interrupt_request & ~mask); > + cpu_mutex_unlock(cpu); > + } > + return; > + } > + > + if (has_cpu_lock) { > + cpu_mutex_unlock(cpu); > } > - cpu->interrupt_request &= ~mask; > - if (need_lock) { > - qemu_mutex_unlock_iothread(); > + qemu_mutex_lock_iothread(); > + cpu_mutex_lock(cpu); > + atomic_set(&cpu->interrupt_request, cpu->interrupt_request & ~mask); > + qemu_mutex_unlock_iothread(); > + if (!has_cpu_lock) { > + cpu_mutex_unlock(cpu); > } > } Yeah I can see this is pretty ugly but cleaned up by the end of the series. If it's the same sequence as the previous patch I wonder if it's possible to hide the ugliness in a common helper while we transition? Otherwise: Reviewed-by: Alex Bennée <alex.bennee@linaro.org> -- Alex Bennée
diff --git a/include/qom/cpu.h b/include/qom/cpu.h index aeed63a705..a86690c7a5 100644 --- a/include/qom/cpu.h +++ b/include/qom/cpu.h @@ -511,6 +511,43 @@ static inline void cpu_halted_set(CPUState *cpu, uint32_t val) cpu_mutex_unlock(cpu); } +/* + * When sending an interrupt, setters OR the appropriate bit and kick the + * destination vCPU. The latter can then read interrupt_request without + * acquiring the CPU lock, because once the kick-induced completes, they'll read + * an up-to-date interrupt_request. + * Setters always acquire the lock, which guarantees that (1) concurrent + * updates from different threads won't result in data races, and (2) the + * BQL-less CPU loop will always see an up-to-date interrupt_request, since the + * loop holds the CPU lock. + */ +static inline uint32_t cpu_interrupt_request(CPUState *cpu) +{ + return atomic_read(&cpu->interrupt_request); +} + +static inline void cpu_interrupt_request_or(CPUState *cpu, uint32_t mask) +{ + if (cpu_mutex_locked(cpu)) { + atomic_set(&cpu->interrupt_request, cpu->interrupt_request | mask); + return; + } + cpu_mutex_lock(cpu); + atomic_set(&cpu->interrupt_request, cpu->interrupt_request | mask); + cpu_mutex_unlock(cpu); +} + +static inline void cpu_interrupt_request_set(CPUState *cpu, uint32_t val) +{ + if (cpu_mutex_locked(cpu)) { + atomic_set(&cpu->interrupt_request, val); + return; + } + cpu_mutex_lock(cpu); + atomic_set(&cpu->interrupt_request, val); + cpu_mutex_unlock(cpu); +} + static inline void cpu_tb_jmp_cache_clear(CPUState *cpu) { unsigned int i; diff --git a/qom/cpu.c b/qom/cpu.c index bb031a3a6a..ecdf8e7aac 100644 --- a/qom/cpu.c +++ b/qom/cpu.c @@ -98,14 +98,29 @@ static void cpu_common_get_memory_mapping(CPUState *cpu, * BQL here if we need to. cpu_interrupt assumes it is held.*/ void cpu_reset_interrupt(CPUState *cpu, int mask) { - bool need_lock = !qemu_mutex_iothread_locked(); + bool has_bql = qemu_mutex_iothread_locked(); + bool has_cpu_lock = cpu_mutex_locked(cpu); - if (need_lock) { - qemu_mutex_lock_iothread(); + if (has_bql) { + if (has_cpu_lock) { + atomic_set(&cpu->interrupt_request, cpu->interrupt_request & ~mask); + } else { + cpu_mutex_lock(cpu); + atomic_set(&cpu->interrupt_request, cpu->interrupt_request & ~mask); + cpu_mutex_unlock(cpu); + } + return; + } + + if (has_cpu_lock) { + cpu_mutex_unlock(cpu); } - cpu->interrupt_request &= ~mask; - if (need_lock) { - qemu_mutex_unlock_iothread(); + qemu_mutex_lock_iothread(); + cpu_mutex_lock(cpu); + atomic_set(&cpu->interrupt_request, cpu->interrupt_request & ~mask); + qemu_mutex_unlock_iothread(); + if (!has_cpu_lock) { + cpu_mutex_unlock(cpu); } }
Add a comment about how atomic_read works here. The comment refers to a "BQL-less CPU loop", which will materialize toward the end of this series. Note that the modifications to cpu_reset_interrupt are there to avoid deadlock during the CPU lock transition; once that is complete, cpu_interrupt_request will be simple again. Signed-off-by: Emilio G. Cota <cota@braap.org> --- include/qom/cpu.h | 37 +++++++++++++++++++++++++++++++++++++ qom/cpu.c | 27 +++++++++++++++++++++------ 2 files changed, 58 insertions(+), 6 deletions(-)