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From: Xiao Guangrong <guangrong.xiao@gmail.com>
Message-ID: <b5ac1a38-7b42-f171-1065-0c3ebf245e5e@gmail.com>
Date: Fri, 29 Jun 2018 15:47:46 +0800
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Subject: Re: [Qemu-devel] [PATCH 09/12] ring: introduce lockless ring buffer
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To: Jason Wang <jasowang@redhat.com>, pbonzini@redhat.com, mst@redhat.com, mtosatti@redhat.com
Cc: qemu-devel@nongnu.org, kvm@vger.kernel.org, dgilbert@redhat.com, peterx@redhat.com, jiang.biao2@zte.com.cn, wei.w.wang@intel.com, Xiao Guangrong <xiaoguangrong@tencent.com>



On 06/29/2018 02:15 PM, Jason Wang wrote:
> 
> 
> On 2018年06月29日 11:59, Xiao Guangrong wrote:
>>
>>
>> On 06/28/2018 09:36 PM, Jason Wang wrote:
>>>
>>>
>>> On 2018年06月04日 17:55, guangrong.xiao@gmail.com wrote:
>>>> From: Xiao Guangrong<xiaoguangrong@tencent.com>
>>>>
>>>> It's the simple lockless ring buffer implement which supports both
>>>> single producer vs. single consumer and multiple producers vs.
>>>> single consumer.
>>>>
>>
>>>> Finally, it fetches the valid data out, set the entry to the initialized
>>>> state and update ring->out to make the entry be usable to the producer:
>>>>
>>>>        data = *entry;
>>>>        *entry = NULL;
>>>>        ring->out++;
>>>>
>>>> Memory barrier is omitted here, please refer to the comment in the code.
>>>>
>>>> (1)https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/include/linux/kfifo.h
>>>> (2)http://dpdk.org/doc/api/rte__ring_8h.html
>>>>
>>>> Signed-off-by: Xiao Guangrong<xiaoguangrong@tencent.com>
>>>> ---
>>>
>>> May I ask why you need a MPSC ring here? Can we just use N SPSC ring for submitting pages and another N SPSC ring for passing back results?
>>
>> Sure.
>>
>> We had this option in our mind, however, it is not scalable which will slow
>> the main thread down, instead, we'd rather to speed up main thread and move
>> reasonable workload to the threads.
> 
> I'm not quite understand the scalability issue here. Is it because of main thread need go through all N rings (which I think not)?

Yes, it is.

The main thread need to check each single thread and wait
it done one by one...