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[174.89.135.171]) by smtp.gmail.com with ESMTPSA id 3f1490d57ef6-e90495fafbbsm3434819276.26.2025.08.11.08.58.08 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 11 Aug 2025 08:58:09 -0700 (PDT) Date: Mon, 11 Aug 2025 11:58:07 -0400 From: Peter Xu To: Igor Mammedov Cc: qemu-devel@nongnu.org, mst@redhat.com, pbonzini@redhat.com, david@redhat.com, philmd@linaro.org, mtosatti@redhat.com Subject: Re: [PATCH v3 05/10] hpet: make main counter read lock-less Message-ID: References: <20250808120137.2208800-1-imammedo@redhat.com> <20250808120137.2208800-6-imammedo@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20250808120137.2208800-6-imammedo@redhat.com> Received-SPF: pass client-ip=170.10.129.124; envelope-from=peterx@redhat.com; helo=us-smtp-delivery-124.mimecast.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, 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_NONE=-0.0001, RCVD_IN_MSPIKE_H5=0.001, RCVD_IN_MSPIKE_WL=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, RCVD_IN_VALIDITY_SAFE_BLOCKED=0.001, SPF_HELO_PASS=-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: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Fri, Aug 08, 2025 at 02:01:32PM +0200, Igor Mammedov wrote: > Make access to main HPET counter lock-less. > > In unlikely event of an update in progress, readers will busy wait > untill update is finished. > > As result micro benchmark of concurrent reading of HPET counter > with large number of vCPU shows over 80% better (less) latency. > > Signed-off-by: Igor Mammedov Reviewed-by: Peter Xu -- Peter Xu