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From: Richard Henderson <rth@twiddle.net>
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Date: Sat, 24 Sep 2016 13:43:14 -0700
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Subject: Re: [Qemu-devel] [PATCH 16/16] cpus-common: lock-free fast path for
 cpu_exec_start/end
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To: Paolo Bonzini <pbonzini@redhat.com>
Cc: qemu-devel@nongnu.org, serge fdrv <serge.fdrv@gmail.com>, cota@braap.org, alex bennee <alex.bennee@linaro.org>, sergey fedorov <sergey.fedorov@linaro.org>

On 09/24/2016 04:52 AM, Paolo Bonzini wrote:
>
>
> ----- Original Message -----
>> From: "Richard Henderson" <rth@twiddle.net>
>> To: "Paolo Bonzini" <pbonzini@redhat.com>, qemu-devel@nongnu.org
>> Cc: "serge fdrv" <serge.fdrv@gmail.com>, cota@braap.org, "alex bennee" <alex.bennee@linaro.org>, "sergey fedorov"
>> <sergey.fedorov@linaro.org>
>> Sent: Friday, September 23, 2016 8:23:46 PM
>> Subject: Re: [Qemu-devel] [PATCH 16/16] cpus-common: lock-free fast path for cpu_exec_start/end
>>
>> On 09/23/2016 12:31 AM, Paolo Bonzini wrote:
>>> +        if (atomic_read(&other_cpu->running)) {
>> ...
>>> +    atomic_set(&cpu->running, true);
>> ...
>>> +            cpu->running = false;
>> ...
>>> +            cpu->running = true;
>>
>> Inconsistent use of atomics.  I don't see that the cpu_list_lock protects the
>> last two lines in any way.
>
> It does:
>
>         qemu_mutex_lock(&qemu_cpu_list_lock);

What I meant is that I don't see that the mutex avoids the need for atomic_set.

> but I can change it anyway to atomic_set.

Thanks,


r~