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Lunev" Cc: qemu-devel@nongnu.org, qemu-block@nongnu.org, Vladimir Sementsov-Ogievskiy , John Snow , Andrey Drobyshev Subject: Re: [PATCH v4 11/12] util/co-shared-resource: skip the mutex for an empty request Message-ID: References: <20261030010613.1612771-1-den@openvz.org> <20261030010613.1612771-12-den@openvz.org> X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20261030010613.1612771-12-den@openvz.org> User-Agent: NeoMutt/20260616 X-Scanned-By: MIMEDefang 3.0 on 10.30.177.17 Received-SPF: pass client-ip=170.10.133.124; envelope-from=eblake@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -27 X-Spam_score: -2.8 X-Spam_bar: -- X-Spam_report: (-2.8 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=unavailable autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: qemu development List-Archive: List-Post: List-Help: List-Subscribe: , Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org X-Spam-Status: No, score=-17.3 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_PASS, SPF_PASS,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=4.0.1 X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 On Fri, Oct 30, 2026 at 02:06:11AM +0100, Denis V. Lunev wrote: > From: Denis V. Lunev > > Getting or putting nothing cannot change the pool, yet both calls take > the mutex, and co_put_to_shres() also wakes every waiter to find the > pool unchanged. Return early when n is zero. > > block-copy is about to reserve nothing for write-zeroes tasks the target > serves without a buffer, which makes such calls the common case for a > mostly-zero image. > > Suggested-by: Vladimir Sementsov-Ogievskiy > Signed-off-by: Denis V. Lunev > CC: Vladimir Sementsov-Ogievskiy > CC: John Snow > CC: Andrey Drobyshev > --- > util/qemu-co-shared-resource.c | 8 ++++++++ > 1 file changed, 8 insertions(+) Reviewed-by: Eric Blake -- Eric Blake, Principal Software Engineer Red Hat, Inc. Virtualization: qemu.org | libguestfs.org