Re: [PATCH v3 2/5] util: introduce threaded workqueue

From: Xiao Guangrong <guangrong.xiao@gmail.com>
To: Paolo Bonzini <pbonzini@redhat.com>, "Emilio G. Cota" <cota@braap.org>
Cc: kvm@vger.kernel.org, mst@redhat.com, mtosatti@redhat.com,
	Xiao Guangrong <xiaoguangrong@tencent.com>,
	dgilbert@redhat.com, peterx@redhat.com, qemu-devel@nongnu.org,
	quintela@redhat.com, wei.w.wang@intel.com,
	jiang.biao2@zte.com.cn
Subject: Re: [PATCH v3 2/5] util: introduce threaded workqueue
Date: Tue, 27 Nov 2018 16:31:31 +0800	[thread overview]
Message-ID: <ec16d438-9897-6308-813f-290bf920dd5d@gmail.com> (raw)
In-Reply-To: <e6a87a89-e667-5c8d-9016-1d6c2a65fc6a@redhat.com>

On 11/26/18 6:28 PM, Paolo Bonzini wrote:
> On 26/11/18 09:18, Xiao Guangrong wrote:
>>>
>>>> +static uint64_t get_free_request_bitmap(Threads *threads,
>>>> ThreadLocal *thread)
>>>> +{
>>>> +    uint64_t request_fill_bitmap, request_done_bitmap, result_bitmap;
>>>> +
>>>> +    request_fill_bitmap =
>>>> atomic_rcu_read(&thread->request_fill_bitmap);
>>>> +    request_done_bitmap =
>>>> atomic_rcu_read(&thread->request_done_bitmap);
>>>> +    bitmap_xor(&result_bitmap, &request_fill_bitmap,
>>>> &request_done_bitmap,
>>>> +               threads->thread_requests_nr);
>>>
>>> This is not wrong, but it's a big ugly. Instead, I would:
>>>
>>> - Introduce bitmap_xor_atomic in a previous patch
>>> - Use bitmap_xor_atomic here, getting rid of the rcu reads
>>
>> Hmm, however, we do not need atomic xor operation here... that should be
>> slower than
>> just two READ_ONCE calls.
> 
> Yeah, I'd just go with Guangrong's version.  Alternatively, add
> find_{first,next}_{same,different}_bit functions (whatever subset of the
> 4 you need).

That's good to me. will try it. ;)