From: Tao Cui <cui.tao@linux.dev>
To: guopeng.zhang@linux.dev
Cc: akpm@linux-foundation.org, bsegall@google.com,
dietmar.eggemann@arm.com, hannes@cmpxchg.org,
juri.lelli@redhat.com, kprateek.nayak@amd.com,
linux-kernel@vger.kernel.org, mgorman@suse.de, mingo@redhat.com,
peterz@infradead.org, rostedt@goodmis.org, surenb@google.com,
vincent.guittot@linaro.org, vschneid@redhat.com,
cui.tao@linux.dev, Tao Cui <cuitao@kylinos.cn>
Subject: Re: [PATCH 1/2] sched/psi: Fix long-window growth interpolation
Date: Tue, 28 Jul 2026 16:49:31 +0800 [thread overview]
Message-ID: <20260728084931.2364795-1-cui.tao@linux.dev> (raw)
In-Reply-To: <20260717102824.985950-2-guopeng.zhang@linux.dev>
From: Tao Cui <cuitao@kylinos.cn>
On Fri, Jul 17, 2026 at 3:29 AM Guopeng Zhang <guopeng.zhang@linux.dev> wrote:
>
> From: Guopeng Zhang <zhangguopeng@kylinos.cn>
>
> PSI trigger windows are stored in nanoseconds and can be up to 10
> seconds, but window_update() stores the remaining interval in a u32.
> For example, after 2 seconds have elapsed in a 10-second window, the
> remaining 8,000,000,000 ns is truncated to 3,705,032,704 ns.
>
> Making remaining a u64 avoids the truncation, but the multiplication
> can still overflow before the division. Both win->prev_growth and
> remaining can be close to 10,000,000,000, so their product can exceed
> U64_MAX.
>
> Store the remaining interval in a u64 and use
> mul_u64_u64_div_u64() to calculate the interpolation without
> overflowing the intermediate product.
>
> Fixes: 0e94682b73bf ("psi: introduce psi monitor")
> Signed-off-by: Guopeng Zhang <zhangguopeng@kylinos.cn>
Acked-by: Tao Cui <cuitao@kylinos.cn>
next prev parent reply other threads:[~2026-07-28 8:50 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-07-17 10:28 [PATCH 0/2] sched/psi: Fix trigger time arithmetic Guopeng Zhang
2026-07-17 10:28 ` [PATCH 1/2] sched/psi: Fix long-window growth interpolation Guopeng Zhang
2026-07-27 3:17 ` Suren Baghdasaryan
2026-07-28 8:49 ` Tao Cui [this message]
2026-07-17 10:28 ` [PATCH 2/2] sched/psi: Fix overflow in trigger time conversion on 32-bit Guopeng Zhang
2026-07-27 3:24 ` Suren Baghdasaryan
2026-07-28 8:52 ` Tao Cui
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