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Tue, 05 Aug 2025 15:03:55 -0700 (PDT) Date: Tue, 5 Aug 2025 23:03:53 +0100 From: Chris Bainbridge To: Peter Zijlstra Cc: mingo@redhat.com, juri.lelli@redhat.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, vschneid@redhat.com, clm@meta.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 02/12] sched/deadline: Less agressive dl_server handling Message-ID: References: <20250702114924.091581796@infradead.org> <20250702121158.465086194@infradead.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250702121158.465086194@infradead.org> On Wed, Jul 02, 2025 at 01:49:26PM +0200, Peter Zijlstra wrote: > Chris reported that commit 5f6bd380c7bd ("sched/rt: Remove default > bandwidth control") caused a significant dip in his favourite > benchmark of the day. Simply disabling dl_server cured things. > > His workload hammers the 0->1, 1->0 transitions, and the > dl_server_{start,stop}() overhead kills it -- fairly obviously a bad > idea in hind sight and all that. > > Change things around to only disable the dl_server when there has not > been a fair task around for a whole period. Since the default period > is 1 second, this ensures the benchmark never trips this, overhead > gone. > > Fixes: 557a6bfc662c ("sched/fair: Add trivial fair server") > Reported-by: Chris Mason > Signed-off-by: Peter Zijlstra (Intel) > Link: https://lkml.kernel.org/r/20250520101727.507378961@infradead.org This commit causes almost every boot of my laptop (which is booted from USB flash/SSD drive) to log "sched: DL replenish lagged too much" around 7 seconds in to the boot. Is this expected? Just asking as this is a change in behaviour - I haven't seen this warning before in several years of using this laptop.