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Thu, 06 May 2021 11:22:16 -0700 (PDT) Received: from [192.168.1.11] ([71.212.144.24]) by smtp.gmail.com with ESMTPSA id y64sm2769017pfy.204.2021.05.06.11.22.16 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 06 May 2021 11:22:16 -0700 (PDT) Subject: Re: [PATCH] virtio-blk: Convert QEMUBH callback to "bitops.h" API To: =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= , qemu-devel@nongnu.org References: <20210506155419.1796056-1-philmd@redhat.com> From: Richard Henderson Message-ID: Date: Thu, 6 May 2021 11:22:14 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.7.1 MIME-Version: 1.0 In-Reply-To: <20210506155419.1796056-1-philmd@redhat.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=2607:f8b0:4864:20::52f; envelope-from=richard.henderson@linaro.org; helo=mail-pg1-x52f.google.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-0.001, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Kevin Wolf , Li Hangjing , Sergio Lopez , qemu-block@nongnu.org, Max Reitz , Chai Wen , Stefan Hajnoczi , Xie Yongji Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 5/6/21 8:54 AM, Philippe Mathieu-Daudé wrote: > static void notify_guest_bh(void *opaque) > { > VirtIOBlockDataPlane *s = opaque; > - unsigned nvqs = s->conf->num_queues; > - unsigned long bitmap[BITS_TO_LONGS(nvqs)]; > - unsigned j; > > - memcpy(bitmap, s->batch_notify_vqs, sizeof(bitmap)); > - memset(s->batch_notify_vqs, 0, sizeof(bitmap)); > - > - for (j = 0; j < nvqs; j += BITS_PER_LONG) { > - unsigned long bits = bitmap[j / BITS_PER_LONG]; > - > - while (bits != 0) { > - unsigned i = j + ctzl(bits); > + for (unsigned i = 0; i < s->conf->num_queues; i++) { Is this bitmap dense enough that you want to iterate by index, or is it sparse enough to iterate via find_first_bit/find_next_bit? In either case, leave the copy of s->conf->num_queues to a local variable. r~