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From: Sergey Fedorov <serge.fdrv@gmail.com>
Message-ID: <5748A635.7040808@gmail.com>
Date: Fri, 27 May 2016 22:55:33 +0300
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Subject: Re: [Qemu-devel] [PATCH v6 02/15] seqlock: remove optional mutex
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To: "Emilio G. Cota" <cota@braap.org>, QEMU Developers <qemu-devel@nongnu.org>, MTTCG Devel <mttcg@listserver.greensocs.com>
Cc: =?UTF-8?Q?Alex_Benn=c3=a9e?= <alex.bennee@linaro.org>, Paolo Bonzini <pbonzini@redhat.com>, Richard Henderson <rth@twiddle.net>

On 25/05/16 04:13, Emilio G. Cota wrote:
> This option is unused; besides, it bloats the struct when not needed.
> Let's just let writers define their own locks elsewhere.
>
> Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
> Reviewed-by: Richard Henderson <rth@twiddle.net>
> Signed-off-by: Emilio G. Cota <cota@braap.org>

Reviewed-by: Sergey Fedorov <sergey.fedorov@linaro.org>

> ---
>  cpus.c                 |  2 +-
>  include/qemu/seqlock.h | 10 +---------
>  2 files changed, 2 insertions(+), 10 deletions(-)
>
> diff --git a/cpus.c b/cpus.c
> index cbeb1f6..dd86da5 100644
> --- a/cpus.c
> +++ b/cpus.c
> @@ -619,7 +619,7 @@ int cpu_throttle_get_percentage(void)
>  
>  void cpu_ticks_init(void)
>  {
> -    seqlock_init(&timers_state.vm_clock_seqlock, NULL);
> +    seqlock_init(&timers_state.vm_clock_seqlock);
>      vmstate_register(NULL, 0, &vmstate_timers, &timers_state);
>      throttle_timer = timer_new_ns(QEMU_CLOCK_VIRTUAL_RT,
>                                             cpu_throttle_timer_tick, NULL);
> diff --git a/include/qemu/seqlock.h b/include/qemu/seqlock.h
> index 70b01fd..e673482 100644
> --- a/include/qemu/seqlock.h
> +++ b/include/qemu/seqlock.h
> @@ -19,22 +19,17 @@
>  typedef struct QemuSeqLock QemuSeqLock;
>  
>  struct QemuSeqLock {
> -    QemuMutex *mutex;
>      unsigned sequence;
>  };
>  
> -static inline void seqlock_init(QemuSeqLock *sl, QemuMutex *mutex)
> +static inline void seqlock_init(QemuSeqLock *sl)
>  {
> -    sl->mutex = mutex;
>      sl->sequence = 0;
>  }
>  
>  /* Lock out other writers and update the count.  */
>  static inline void seqlock_write_lock(QemuSeqLock *sl)
>  {
> -    if (sl->mutex) {
> -        qemu_mutex_lock(sl->mutex);
> -    }
>      ++sl->sequence;
>  
>      /* Write sequence before updating other fields.  */
> @@ -47,9 +42,6 @@ static inline void seqlock_write_unlock(QemuSeqLock *sl)
>      smp_wmb();
>  
>      ++sl->sequence;
> -    if (sl->mutex) {
> -        qemu_mutex_unlock(sl->mutex);
> -    }
>  }
>  
>  static inline unsigned seqlock_read_begin(QemuSeqLock *sl)