From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:51966) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1gRC6W-0003Um-84 for qemu-devel@nongnu.org; Mon, 26 Nov 2018 03:18:52 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1gRC6R-00045f-AO for qemu-devel@nongnu.org; Mon, 26 Nov 2018 03:18:52 -0500 Received: from mail-pl1-x642.google.com ([2607:f8b0:4864:20::642]:33889) by eggs.gnu.org with esmtps (TLS1.0:RSA_AES_128_CBC_SHA1:16) (Exim 4.71) (envelope-from ) id 1gRC6N-0003dY-DJ for qemu-devel@nongnu.org; Mon, 26 Nov 2018 03:18:45 -0500 Received: by mail-pl1-x642.google.com with SMTP id f12-v6so13519277plo.1 for ; Mon, 26 Nov 2018 00:18:31 -0800 (PST) References: <20181122072028.22819-1-xiaoguangrong@tencent.com> <20181122072028.22819-3-xiaoguangrong@tencent.com> <20181124001734.GF17229@flamenco> From: Xiao Guangrong Message-ID: <122f7c3b-ebaf-a2c0-3181-cce82d857058@gmail.com> Date: Mon, 26 Nov 2018 16:18:24 +0800 MIME-Version: 1.0 In-Reply-To: <20181124001734.GF17229@flamenco> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH v3 2/5] util: introduce threaded workqueue List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Emilio G. Cota" Cc: pbonzini@redhat.com, mst@redhat.com, mtosatti@redhat.com, qemu-devel@nongnu.org, kvm@vger.kernel.org, dgilbert@redhat.com, peterx@redhat.com, wei.w.wang@intel.com, jiang.biao2@zte.com.cn, eblake@redhat.com, quintela@redhat.com, Xiao Guangrong On 11/24/18 8:17 AM, Emilio G. Cota wrote: > On Thu, Nov 22, 2018 at 15:20:25 +0800, guangrong.xiao@gmail.com 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.