From: Tejun Heo <tj@kernel.org>
To: Tao Cui <cui.tao@linux.dev>
Cc: arighi@nvidia.com, void@manifault.com, changwoo@igalia.com,
michalblk@google.com, liwanwu@kylinos.cn,
sched-ext@lists.linux.dev, linux-kernel@vger.kernel.org,
bpf@vger.kernel.org, Tao Cui <cuitao@kylinos.cn>,
Sashiko <sashiko-bot@kernel.org>
Subject: Re: [PATCH v2 2/2] sched_ext/scx_flatcg: make cgv_node_less() wraparound-safe
Date: Tue, 01 Sep 2026 10:00:05 -1000 [thread overview]
Message-ID: <beadefcfd5ae112a703b2514f6eebf34@kernel.org> (raw)
In-Reply-To: <20260901140343.764080-3-cui.tao@linux.dev>
Hello,
On Tue, Sep 01, 2026 at 10:03:43PM +0800, Tao Cui wrote:
...
> long-running host. At the wrap instant the plain comparison puts the
> wrapped node behind everything else permanently.
Plain < puts the wrapped node at the front. The unwrapped ones get stuck
behind it. Also, each CPU picking a cgroup charges it a full slice, so the
wrap is closer than weeks.
...
> cyclic comparison is valid as an rbtree comparator only because
> cgrp_cap_budget() clamps every node to within max_budget behind
> cvtime_now, so any two nodes are far less than 2^63 apart and the
...
cgrp_cap_budget() only bounds the lag. The lead is bounded by the slice
charge plus pending cvtime_delta on re-insertion.
> Fixes: 7b742aa2c2c9 ("sched_ext: Add a cgroup scheduler which uses flattened hierarchy")
Not in mainline. The upstream commit is a4103eacc2ab.
> + /* wrap-safe: cap_budget keeps nodes within 2^63 of each other */
> + return (s64)(cgc_a->cvtime - cgc_b->cvtime) < 0;
Use time_before() and drop the comment.
Thanks.
--
tejun
next prev parent reply other threads:[~2026-09-01 20:00 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-09-01 14:03 [PATCH v2 0/2] sched_ext: document and enforce vtime ordering constraints Tao Cui
2026-09-01 14:03 ` [PATCH v2 1/2] sched_ext: document the rolling-cursor requirement for dsq_vtime Tao Cui
2026-09-01 19:59 ` Tejun Heo
2026-09-01 14:03 ` [PATCH v2 2/2] sched_ext/scx_flatcg: make cgv_node_less() wraparound-safe Tao Cui
2026-09-01 20:00 ` Tejun Heo [this message]
2026-09-02 1:21 ` Tao Cui
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