From: Juri Lelli <juri.lelli@redhat.com>
To: Kuyo Chang <kuyo.chang@mediatek.com>
Cc: Ingo Molnar <mingo@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
Vincent Guittot <vincent.guittot@linaro.org>,
Dietmar Eggemann <dietmar.eggemann@arm.com>,
Steven Rostedt <rostedt@goodmis.org>,
Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,
Valentin Schneider <vschneid@redhat.com>,
Matthias Brugger <matthias.bgg@gmail.com>,
AngeloGioacchino Del Regno
<angelogioacchino.delregno@collabora.com>,
jstultz <jstultz@google.com>,
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
Date: Mon, 16 Jun 2025 16:03:20 +0200 [thread overview]
Message-ID: <aFAkKGs5h6kfXYnO@jlelli-thinkpadt14gen4.remote.csb> (raw)
In-Reply-To: <20250614020524.631521-1-kuyo.chang@mediatek.com>
Hello,
On 14/06/25 10:04, Kuyo Chang wrote:
> From: kuyo chang <kuyo.chang@mediatek.com>
>
> [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 <kuyo.chang@mediatek.com>
> ---
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 <juri.lelli@redhat.com>
Thanks!
Juri
next prev parent reply other threads:[~2025-06-16 16:38 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-06-14 2:04 [PATCH 1/1] sched/deadline: Fix fair_server runtime calculation formula Kuyo Chang
2025-06-14 2:35 ` John Stultz
2025-06-16 14:03 ` Juri Lelli [this message]
2025-06-17 8:55 ` Peter Zijlstra
2025-06-17 12:33 ` Juri Lelli
2025-06-17 14:14 ` Peter Zijlstra
2025-06-17 14:23 ` Juri Lelli
2025-06-17 14:41 ` Kuyo Chang (張建文)
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