From mboxrd@z Thu Jan 1 00:00:00 1970 From: Xiao Guangrong Subject: Re: [PATCH v3 2/5] util: introduce threaded workqueue Date: Tue, 27 Nov 2018 16:31:31 +0800 Message-ID: References: <20181122072028.22819-1-xiaoguangrong@tencent.com> <20181122072028.22819-3-xiaoguangrong@tencent.com> <20181124001734.GF17229@flamenco> <122f7c3b-ebaf-a2c0-3181-cce82d857058@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Cc: kvm@vger.kernel.org, mst@redhat.com, mtosatti@redhat.com, Xiao Guangrong , dgilbert@redhat.com, peterx@redhat.com, qemu-devel@nongnu.org, quintela@redhat.com, wei.w.wang@intel.com, jiang.biao2@zte.com.cn To: Paolo Bonzini , "Emilio G. Cota" Return-path: In-Reply-To: Content-Language: en-US List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+gceq-qemu-devel2=m.gmane.org@nongnu.org Sender: "Qemu-devel" List-Id: kvm.vger.kernel.org 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. ;)