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Wysocki" , Thomas Gleixner , linux-kernel@vger.kernel.org Subject: Re: [PATCH] sched/idle: disable tick in idle=poll idle entry Message-ID: References: <20230608083400.GH998233@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230608083400.GH998233@hirez.programming.kicks-ass.net> X-Scanned-By: MIMEDefang 3.1 on 10.11.54.2 X-Spam-Status: No, score=-0.5 required=5.0 tests=BAYES_00,DATE_IN_PAST_03_06, DKIMWL_WL_HIGH,DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF, RCVD_IN_DNSWL_NONE,SPF_HELO_NONE,SPF_NONE,T_SCC_BODY_TEXT_LINE, URIBL_BLOCKED autolearn=no autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jun 08, 2023 at 10:34:00AM +0200, Peter Zijlstra wrote: > On Wed, Jun 07, 2023 at 10:10:46PM -0300, Marcelo Tosatti wrote: > > > > Commit a5183862e76fdc25f36b39c2489b816a5c66e2e5 > > ("tick/nohz: Conditionally restart tick on idle exit") allows > > a nohz_full CPU to enter idle and return from it with the > > scheduler tick disabled (since the tick might be undesired noise). > > > > The idle=poll case still unconditionally restarts the tick when entering > > idle. > > > > To reduce the noise for that case as well, stop the tick when entering > > idle, for the idle=poll case. > > > > tick_nohz_idle_exit (called if the NEED_RESCHED bit is set) > > is responsible for re-enabling the tick when necessary. > > Who cares and why? Systems that use isolcpus/nohz_full, and use idle=poll to avoid sleeping. For example: https://github.com/intel/FlexRAN/blob/master/README.md More specifically, the case which HLTs (via nanosleep usually) is: https://www.isa.org/intech-home/2022/february-2022/departments/what-you-may-not-know-about-softplcs Can add this to the next version of the patch (unless you have any other comments). Thanks.