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Date: Wed, 17 Dec 2014 11:28:56 +0100
From: Alexander Graf <agraf@suse.de>
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Subject: Re: [Qemu-devel] [RFC PATCH] target-arm: protect cpu_exclusive_*.
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To: Frederic Konrad <fred.konrad@greensocs.com>, Peter Maydell <peter.maydell@linaro.org>
Cc: mttcg@listserver.greensocs.com, Paolo Bonzini <pbonzini@redhat.com>, Mark Burton <mark.burton@greensocs.com>, QEMU Developers <qemu-devel@nongnu.org>, =?UTF-8?B?TGx1w61zIFZpbGFub3Zh?= <vilanova@ac.upc.edu>



On 17.12.14 11:27, Frederic Konrad wrote:
> On 16/12/2014 17:37, Peter Maydell wrote:
>> On 16 December 2014 at 09:13,  <fred.konrad@greensocs.com> wrote:
>>> From: KONRAD Frederic <fred.konrad@greensocs.com>
>>>
>>> This adds a lock to avoid multiple exclusive access at the same time
>>> in case of
>>> TCG multithread.
> Hi Peter,
> 
>> This feels to me like it's not really possible to review on
>> its own, since you can't see how it fits into the design of
>> the rest of the multithreading support.
> true the only thing we observe is that it didn't change anything right now.
> 
>> The other approach here rather than having a pile of mutexes
>> in the target-* code would be to have TCG IR support for
>> "begin critical section"/"end critical section". Then you
>> could have the main loop ensure that no other CPU is running
>> at the same time as the critical-section code. (linux-user
>> already has an ad-hoc implementation of this for the
>> exclusives.)
>>
>> -- PMM
>>
> What do you mean by TCG IR?

TCP ops. The nice thing is that TCG could translate those into
transactions if the host supports them as well.


Alex