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([2001:b07:6468:f312:b903:6d6f:a447:e464]) by smtp.gmail.com with ESMTPSA id w18sm4227122wmc.9.2019.10.01.09.38.50 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 01 Oct 2019 09:38:51 -0700 (PDT) Subject: Re: [PATCH] cpus: kick all vCPUs when running thread=single To: =?UTF-8?Q?Alex_Benn=c3=a9e?= , qemu-devel@nongnu.org References: <20191001160426.26644-1-alex.bennee@linaro.org> From: Paolo Bonzini Openpgp: preference=signencrypt Message-ID: <5582c91e-ac0e-9f74-a3de-82f7fe25fadd@redhat.com> Date: Tue, 1 Oct 2019 18:38:49 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <20191001160426.26644-1-alex.bennee@linaro.org> Content-Language: en-US X-MC-Unique: 5JRVJk2ePTKLTHmMbrE-dg-1 X-Mimecast-Spam-Score: 0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 205.139.110.120 X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Peter Maydell , Doug Gale , Richard Henderson Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 01/10/19 18:04, Alex Benn=C3=A9e wrote: > qemu_cpu_kick is used for a number of reasons including to indicate > there is work to be done. However when thread=3Dsingle the old > qemu_cpu_kick_rr_cpu only advanced the vCPU to the next executing one > which can lead to a hang in the case that: >=20 > a) the kick is from outside the vCPUs (e.g. iothread) > b) the timers are paused (i.e. iothread calling run_on_cpu) >=20 > To avoid this lets split qemu_cpu_kick_rr into two functions. One for > the timer which continues to advance to the next timeslice and another > for all other kicks. >=20 > Signed-off-by: Alex Benn=C3=A9e > Cc: Doug Gale > Cc: Paolo Bonzini > Cc: Peter Maydell > --- > cpus.c | 24 ++++++++++++++++++------ > 1 file changed, 18 insertions(+), 6 deletions(-) Looks good to me. Single-threaded TCG is not going to have high vCPU counts anyway. Paolo > diff --git a/cpus.c b/cpus.c > index d2c61ff155..bee7209134 100644 > --- a/cpus.c > +++ b/cpus.c > @@ -949,8 +949,8 @@ static inline int64_t qemu_tcg_next_kick(void) > return qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL) + TCG_KICK_PERIOD; > } > =20 > -/* Kick the currently round-robin scheduled vCPU */ > -static void qemu_cpu_kick_rr_cpu(void) > +/* Kick the currently round-robin scheduled vCPU to next */ > +static void qemu_cpu_kick_rr_next_cpu(void) > { > CPUState *cpu; > do { > @@ -961,6 +961,16 @@ static void qemu_cpu_kick_rr_cpu(void) > } while (cpu !=3D atomic_mb_read(&tcg_current_rr_cpu)); > } > =20 > +/* Kick all RR vCPUs */ > +static void qemu_cpu_kick_rr_cpus(void) > +{ > + CPUState *cpu; > + > + CPU_FOREACH(cpu) { > + cpu_exit(cpu); > + }; > +} > + > static void do_nothing(CPUState *cpu, run_on_cpu_data unused) > { > } > @@ -993,7 +1003,7 @@ void qemu_timer_notify_cb(void *opaque, QEMUClockTyp= e type) > static void kick_tcg_thread(void *opaque) > { > timer_mod(tcg_kick_vcpu_timer, qemu_tcg_next_kick()); > - qemu_cpu_kick_rr_cpu(); > + qemu_cpu_kick_rr_next_cpu(); > } > =20 > static void start_tcg_kick_timer(void) > @@ -1828,9 +1838,11 @@ void qemu_cpu_kick(CPUState *cpu) > { > qemu_cond_broadcast(cpu->halt_cond); > if (tcg_enabled()) { > - cpu_exit(cpu); > - /* NOP unless doing single-thread RR */ > - qemu_cpu_kick_rr_cpu(); > + if (qemu_tcg_mttcg_enabled()) { > + cpu_exit(cpu); > + } else { > + qemu_cpu_kick_rr_cpus(); > + } > } else { > if (hax_enabled()) { > /* >=20