Re: [PATCH v2 1/5] system/cpus: rename qemu_mutex_lock_iothread() to bql_lock()

[Akihiko Odaki <akihiko.odaki@xxxxxxxxxx>]

On 2023/12/13 0:39, Stefan Hajnoczi wrote:
> The Big QEMU Lock (BQL) has many names and they are confusing. The
> actual QemuMutex variable is called qemu_global_mutex but it's commonly
> referred to as the BQL in discussions and some code comments. The
> locking APIs, however, are called qemu_mutex_lock_iothread() and
> qemu_mutex_unlock_iothread().
>
> The "iothread" name is historic and comes from when the main thread was
> split into into KVM vcpu threads and the "iothread" (now called the main
> loop thread). I have contributed to the confusion myself by introducing
> a separate --object iothread, a separate concept unrelated to the BQL.
>
> The "iothread" name is no longer appropriate for the BQL. Rename the
> locking APIs to:
> - void bql_lock(void)
> - void bql_unlock(void)
> - bool bql_locked(void)
>
> There are more APIs with "iothread" in their names. Subsequent patches
> will rename them. There are also comments and documentation that will be
> updated in later patches.
>
> Signed-off-by: Stefan Hajnoczi <stefanha@xxxxxxxxxx>
> Reviewed-by: Paul Durrant <paul@xxxxxxx>
> Acked-by: Fabiano Rosas <farosas@xxxxxxx>
> Acked-by: David Woodhouse <dwmw@xxxxxxxxxxxx>
> Reviewed-by: Cédric Le Goater <clg@xxxxxxxx>
> Acked-by: Peter Xu <peterx@xxxxxxxxxx>
> Acked-by: Eric Farman <farman@xxxxxxxxxxxxx>
> Reviewed-by: Harsh Prateek Bora <harshpb@xxxxxxxxxxxxx>
> ---
>   include/block/aio-wait.h             |   2 +-
>   include/qemu/main-loop.h             |  40 ++++-----
>   include/qemu/thread.h                |   2 +-
>   accel/accel-blocker.c                |  10 +--
>   accel/dummy-cpus.c                   |   8 +-
>   accel/hvf/hvf-accel-ops.c            |   4 +-
>   accel/kvm/kvm-accel-ops.c            |   4 +-
>   accel/kvm/kvm-all.c                  |  22 ++---
>   accel/tcg/cpu-exec.c                 |  26 +++---
>   accel/tcg/cputlb.c                   |  16 ++--
>   accel/tcg/tcg-accel-ops-icount.c     |   4 +-
>   accel/tcg/tcg-accel-ops-mttcg.c      |  12 +--
>   accel/tcg/tcg-accel-ops-rr.c         |  14 ++--
>   accel/tcg/tcg-accel-ops.c            |   2 +-
>   accel/tcg/translate-all.c            |   2 +-
>   cpu-common.c                         |   4 +-
>   dump/dump.c                          |   4 +-
>   hw/core/cpu-common.c                 |   6 +-
>   hw/i386/intel_iommu.c                |   6 +-
>   hw/i386/kvm/xen_evtchn.c             |  16 ++--
>   hw/i386/kvm/xen_overlay.c            |   2 +-
>   hw/i386/kvm/xen_xenstore.c           |   2 +-
>   hw/intc/arm_gicv3_cpuif.c            |   2 +-
>   hw/intc/s390_flic.c                  |  18 ++--
>   hw/misc/edu.c                        |   4 +-
>   hw/misc/imx6_src.c                   |   2 +-
>   hw/misc/imx7_src.c                   |   2 +-
>   hw/net/xen_nic.c                     |   8 +-
>   hw/ppc/pegasos2.c                    |   2 +-
>   hw/ppc/ppc.c                         |   4 +-
>   hw/ppc/spapr.c                       |   2 +-
>   hw/ppc/spapr_rng.c                   |   4 +-
>   hw/ppc/spapr_softmmu.c               |   4 +-
>   hw/remote/mpqemu-link.c              |  20 ++---
>   hw/remote/vfio-user-obj.c            |   2 +-
>   hw/s390x/s390-skeys.c                |   2 +-
>   migration/block-dirty-bitmap.c       |   4 +-
>   migration/block.c                    |  16 ++--
>   migration/colo.c                     |  60 +++++++-------
>   migration/dirtyrate.c                |  12 +--
>   migration/migration.c                |  52 ++++++------
>   migration/ram.c                      |  12 +--
>   replay/replay-internal.c             |   2 +-
>   semihosting/console.c                |   8 +-
>   stubs/iothread-lock.c                |   6 +-
>   system/cpu-throttle.c                |   4 +-
>   system/cpus.c                        |  51 ++++++------
>   system/dirtylimit.c                  |   4 +-
>   system/memory.c                      |   2 +-
>   system/physmem.c                     |   8 +-
>   system/runstate.c                    |   2 +-
>   system/watchpoint.c                  |   4 +-
>   target/arm/arm-powerctl.c            |  14 ++--
>   target/arm/helper.c                  |   4 +-
>   target/arm/hvf/hvf.c                 |   8 +-
>   target/arm/kvm.c                     |   4 +-
>   target/arm/kvm64.c                   |   4 +-
>   target/arm/ptw.c                     |   6 +-
>   target/arm/tcg/helper-a64.c          |   8 +-
>   target/arm/tcg/m_helper.c            |   6 +-
>   target/arm/tcg/op_helper.c           |  24 +++---
>   target/arm/tcg/psci.c                |   2 +-
>   target/hppa/int_helper.c             |   8 +-
>   target/i386/hvf/hvf.c                |   6 +-
>   target/i386/kvm/hyperv.c             |   4 +-
>   target/i386/kvm/kvm.c                |  28 +++----
>   target/i386/kvm/xen-emu.c            |  14 ++--
>   target/i386/nvmm/nvmm-accel-ops.c    |   4 +-
>   target/i386/nvmm/nvmm-all.c          |  20 ++---
>   target/i386/tcg/sysemu/fpu_helper.c  |   6 +-
>   target/i386/tcg/sysemu/misc_helper.c |   4 +-
>   target/i386/whpx/whpx-accel-ops.c    |   4 +-
>   target/i386/whpx/whpx-all.c          |  24 +++---
>   target/loongarch/csr_helper.c        |   4 +-
>   target/mips/kvm.c                    |   4 +-
>   target/mips/tcg/sysemu/cp0_helper.c  |   4 +-
>   target/openrisc/sys_helper.c         |  16 ++--
>   target/ppc/excp_helper.c             |  12 +--
>   target/ppc/kvm.c                     |   4 +-
>   target/ppc/misc_helper.c             |   8 +-
>   target/ppc/timebase_helper.c         |   8 +-
>   target/s390x/kvm/kvm.c               |   4 +-
>   target/s390x/tcg/misc_helper.c       | 118 +++++++++++++--------------
>   target/sparc/int32_helper.c          |   2 +-
>   target/sparc/int64_helper.c          |   6 +-
>   target/sparc/win_helper.c            |  20 ++---
>   target/xtensa/exc_helper.c           |   8 +-
>   ui/spice-core.c                      |   4 +-
>   util/async.c                         |   2 +-
>   util/main-loop.c                     |   8 +-
>   util/qsp.c                           |   6 +-
>   util/rcu.c                           |  14 ++--
>   audio/coreaudio.m                    |   4 +-
>   memory_ldst.c.inc                    |  18 ++--
>   target/i386/hvf/README.md            |   2 +-
>   ui/cocoa.m                           |  50 ++++++------
>   96 files changed, 530 insertions(+), 529 deletions(-)
>
> diff --git a/include/block/aio-wait.h b/include/block/aio-wait.h
> index 5449b6d742..d22ca24329 100644
> --- a/include/block/aio-wait.h
> +++ b/include/block/aio-wait.h
> @@ -151,7 +151,7 @@ static inline bool in_aio_context_home_thread(AioContext 
> *ctx)
>       }
>   
>       if (ctx == qemu_get_aio_context()) {
> -        return qemu_mutex_iothread_locked();
> +        return bql_locked();
>       } else {
>           return false;
>       }
> diff --git a/include/qemu/main-loop.h b/include/qemu/main-loop.h
> index 68e70e61aa..596a206acd 100644
> --- a/include/qemu/main-loop.h
> +++ b/include/qemu/main-loop.h
> @@ -248,19 +248,19 @@ GSource *iohandler_get_g_source(void);
>   AioContext *iohandler_get_aio_context(void);
>   
>   /**
> - * qemu_mutex_iothread_locked: Return lock status of the main loop mutex.
> + * bql_locked: Return lock status of the Big QEMU Lock (BQL)
>    *
> - * The main loop mutex is the coarsest lock in QEMU, and as such it
> + * The Big QEMU Lock (BQL) 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.
> + * thread is running within the BQL.
>    *
>    * This function should never be used in the block layer, because
>    * unit tests, block layer tools and qemu-storage-daemon do not
>    * have a BQL.
>    * Please instead refer to qemu_in_main_thread().
>    */
> -bool qemu_mutex_iothread_locked(void);
> +bool bql_locked(void);
>   
>   /**
>    * qemu_in_main_thread: return whether it's possible to safely access
> @@ -312,58 +312,58 @@ bool qemu_in_main_thread(void);
>       } while (0)
>   
>   /**
> - * qemu_mutex_lock_iothread: Lock the main loop mutex.
> + * bql_lock: Lock the Big QEMU Lock (BQL).
>    *
> - * This function locks the main loop mutex.  The mutex is taken by
> + * This function locks the Big QEMU Lock (BQL).  The lock is taken by
>    * main() in vl.c and always taken except while waiting on
> - * external events (such as with select).  The mutex should be taken
> + * external events (such as with select).  The lock should be taken
>    * by threads other than the main loop thread when calling
>    * qemu_bh_new(), qemu_set_fd_handler() and basically all other
>    * functions documented in this file.
>    *
> - * NOTE: tools currently are single-threaded and qemu_mutex_lock_iothread
> + * NOTE: tools currently are single-threaded and bql_lock
>    * is a no-op there.
>    */
> -#define qemu_mutex_lock_iothread()                      \
> -    qemu_mutex_lock_iothread_impl(__FILE__, __LINE__)
> -void qemu_mutex_lock_iothread_impl(const char *file, int line);
> +#define bql_lock()                      \
> +    bql_lock_impl(__FILE__, __LINE__)
This line break is no longer necessary.