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Mon, 16 Jun 2025 07:03:27 -0700 (PDT) X-Google-Smtp-Source: AGHT+IGhnN5lqHyekM9U5mFuJ4VnEOh6SefVAzY1bT/B5jogeMQLSgptuYNFVoJKZP5a2pKpaGM6cQ== X-Received: by 2002:a5d:64c9:0:b0:3a4:dde7:ee12 with SMTP id ffacd0b85a97d-3a572e9e01cmr8626772f8f.53.1750082605375; Mon, 16 Jun 2025 07:03:25 -0700 (PDT) Received: from jlelli-thinkpadt14gen4.remote.csb ([151.29.151.199]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3a568a54d7fsm11345085f8f.18.2025.06.16.07.03.23 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 16 Jun 2025 07:03:24 -0700 (PDT) Date: Mon, 16 Jun 2025 16:03:20 +0200 From: Juri Lelli To: Kuyo Chang Cc: Ingo Molnar , Peter Zijlstra , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Valentin Schneider , Matthias Brugger , AngeloGioacchino Del Regno , jstultz , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-mediatek@lists.infradead.org Subject: Re: [PATCH 1/1] sched/deadline: Fix fair_server runtime calculation formula Message-ID: References: <20250614020524.631521-1-kuyo.chang@mediatek.com> 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: <20250614020524.631521-1-kuyo.chang@mediatek.com> Hello, On 14/06/25 10:04, Kuyo Chang wrote: > From: kuyo chang > > [Symptom] > The calculation formula for fair_server runtime is based on > Frequency/CPU scale-invariance. > This will cause excessive RT latency (expect absolute time). > > [Analysis] > Consider the following case under a Big.LITTLE architecture: > > Assume the runtime is : 50,000,000 ns, and FIE/CIE as below > FIE: 100 > CIE:50 > First by FIE, the runtime is scaled to 50,000,000 * 100 >> 10 = 4,882,812 > Then by CIE, it is further scaled to 4,882,812 * 50 >> 10 = 238,418. > > So it will scaled to 238,418 ns. > > [Solution] > The runtime for fair_server should be absolute time > asis RT bandwidth control. > Fix the runtime calculation formula for the fair_server. > > Signed-off-by: kuyo chang > --- Right, I would agree we don't actually want to scale fair_server runtime by frequency/capacity. Your change looks good to me. Acked-by: Juri Lelli Thanks! Juri