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Date: Tue, 11 Aug 2015 23:34:38 +0200
From: Frederic Konrad <fred.konrad@greensocs.com>
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Subject: Re: [Qemu-devel] [RFC PATCH V7 09/19] Drop global lock during TCG
	code execution
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To: =?UTF-8?B?QWxleCBCZW5uw6ll?= <alex.bennee@linaro.org>, Paolo Bonzini <pbonzini@redhat.com>
Cc: mttcg@greensocs.com, guillaume.delbergue@greensocs.com, mark.burton@greensocs.com, qemu-devel@nongnu.org, a.rigo@virtualopensystems.com

On 11/08/2015 22:12, Alex Benn=C3=A9e wrote:
> Paolo Bonzini <pbonzini@redhat.com> writes:
>
>> On 10/08/2015 17:27, fred.konrad@greensocs.com wrote:
>>>   void qemu_mutex_lock_iothread(void)
>>>   {
>>> -    atomic_inc(&iothread_requesting_mutex);
>>> -    /* In the simple case there is no need to bump the VCPU thread o=
ut of
>>> -     * TCG code execution.
>>> -     */
>>> -    if (!tcg_enabled() || qemu_in_vcpu_thread() ||
>>> -        !first_cpu || !first_cpu->thread) {
>>> -        qemu_mutex_lock(&qemu_global_mutex);
>>> -        atomic_dec(&iothread_requesting_mutex);
>>> -    } else {
>>> -        if (qemu_mutex_trylock(&qemu_global_mutex)) {
>>> -            qemu_cpu_kick_thread(first_cpu);
>>> -            qemu_mutex_lock(&qemu_global_mutex);
>>> -        }
>>> -        atomic_dec(&iothread_requesting_mutex);
>>> -        qemu_cond_broadcast(&qemu_io_proceeded_cond);
>>> -    }
>>> -    iothread_locked =3D true;
>> "iothread_locked =3D true" must be kept.  Otherwise... yay! :)
>>
> Also if qemu_cond_broadcast(&qemu_io_proceeded_cond) is being dropped
> there is no point keeping the guff around in qemu_tcg_wait_io_event.
>
Yes good point.

BTW this leads to high consumption of host CPU eg: 100% per VCPU thread a=
s
the VCPUs thread are no longer waiting for qemu_io_proceeded_cond.

Fred