From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:49352) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bNiBm-0001Kc-Fx for qemu-devel@nongnu.org; Thu, 14 Jul 2016 11:04:38 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1bNiBh-0004on-Rd for qemu-devel@nongnu.org; Thu, 14 Jul 2016 11:04:33 -0400 Received: from mail-wm0-x22c.google.com ([2a00:1450:400c:c09::22c]:36963) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bNiBg-0004oK-TQ for qemu-devel@nongnu.org; Thu, 14 Jul 2016 11:04:29 -0400 Received: by mail-wm0-x22c.google.com with SMTP id i5so116858306wmg.0 for ; Thu, 14 Jul 2016 08:04:28 -0700 (PDT) References: <1467839703-11733-1-git-send-email-sergey.fedorov@linaro.org> <1467839703-11733-8-git-send-email-sergey.fedorov@linaro.org> From: Alex =?utf-8?Q?Benn=C3=A9e?= In-reply-to: <1467839703-11733-8-git-send-email-sergey.fedorov@linaro.org> Date: Thu, 14 Jul 2016 16:04:30 +0100 Message-ID: <87eg6w45xd.fsf@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Subject: Re: [Qemu-devel] [RFC v2 07/11] linux-user: Rework exclusive operation mechanism List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Sergey Fedorov Cc: qemu-devel@nongnu.org, MTTCG Devel , KONRAD =?utf-8?B?RnLDqWTDqXJpYw==?= , Alvise Rigo , "Emilio G. Cota" , Paolo Bonzini , Richard Henderson , Peter Maydell , Sergey Fedorov , Riku Voipio Sergey Fedorov writes: > From: Sergey Fedorov > > A single variable 'pending_cpus' was used for both counting currently > running CPUs and for signalling the pending exclusive operation request. > > To prepare for supporting operations which requires a quiescent state, > like translation buffer flush, it is useful to keep a counter of > currently running CPUs always up to date. > > Use a separate variable 'tcg_pending_threads' to count for currently > running CPUs and a separate variable 'exclusive_pending' to indicate > that there's an exclusive operation pending. > > Signed-off-by: Sergey Fedorov > Signed-off-by: Sergey Fedorov > --- > > Changes in v2: > - Rename 'tcg_pending_cpus' to 'tcg_pending_threads' Reviewed-by: Alex Bennée > > --- > linux-user/main.c | 24 ++++++++++++------------ > 1 file changed, 12 insertions(+), 12 deletions(-) > > diff --git a/linux-user/main.c b/linux-user/main.c > index bdbda693cc5f..5ff0b20bad89 100644 > --- a/linux-user/main.c > +++ b/linux-user/main.c > @@ -112,7 +112,8 @@ static QemuMutex cpu_list_mutex; > static QemuMutex exclusive_lock; > static QemuCond exclusive_cond; > static QemuCond exclusive_resume; > -static int pending_cpus; > +static bool exclusive_pending; > +static int tcg_pending_threads; > > void qemu_init_cpu_loop(void) > { > @@ -142,7 +143,8 @@ void fork_end(int child) > QTAILQ_REMOVE(&cpus, cpu, node); > } > } > - pending_cpus = 0; > + tcg_pending_threads = 0; > + exclusive_pending = false; > qemu_mutex_init(&exclusive_lock); > qemu_mutex_init(&cpu_list_mutex); > qemu_cond_init(&exclusive_cond); > @@ -159,7 +161,7 @@ void fork_end(int child) > must be held. */ > static inline void exclusive_idle(void) > { > - while (pending_cpus) { > + while (exclusive_pending) { > qemu_cond_wait(&exclusive_resume, &exclusive_lock); > } > } > @@ -173,15 +175,14 @@ static inline void start_exclusive(void) > qemu_mutex_lock(&exclusive_lock); > exclusive_idle(); > > - pending_cpus = 1; > + exclusive_pending = true; > /* Make all other cpus stop executing. */ > CPU_FOREACH(other_cpu) { > if (other_cpu->running) { > - pending_cpus++; > cpu_exit(other_cpu); > } > } > - if (pending_cpus > 1) { > + while (tcg_pending_threads) { > qemu_cond_wait(&exclusive_cond, &exclusive_lock); > } > } > @@ -189,7 +190,7 @@ static inline void start_exclusive(void) > /* Finish an exclusive operation. */ > static inline void __attribute__((unused)) end_exclusive(void) > { > - pending_cpus = 0; > + exclusive_pending = false; > qemu_cond_broadcast(&exclusive_resume); > qemu_mutex_unlock(&exclusive_lock); > } > @@ -200,6 +201,7 @@ static inline void cpu_exec_start(CPUState *cpu) > qemu_mutex_lock(&exclusive_lock); > exclusive_idle(); > cpu->running = true; > + tcg_pending_threads++; > qemu_mutex_unlock(&exclusive_lock); > } > > @@ -208,11 +210,9 @@ static inline void cpu_exec_end(CPUState *cpu) > { > qemu_mutex_lock(&exclusive_lock); > cpu->running = false; > - if (pending_cpus > 1) { > - pending_cpus--; > - if (pending_cpus == 1) { > - qemu_cond_signal(&exclusive_cond); > - } > + tcg_pending_threads--; > + if (!tcg_pending_threads) { > + qemu_cond_signal(&exclusive_cond); > } > exclusive_idle(); > qemu_mutex_unlock(&exclusive_lock); -- Alex Bennée