linux-kernel - Re: [RFC PATCH] locking/percpu-rwsem: do not do lock handoff in percpu_up

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Date: Tue, 30 Jan 2024 19:41:56 +0800
From: Hillf Danton <hdanton@...a.com>
To: Benjamin Segall <bsegall@...gle.com>
Cc: Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>,
	Will Deacon <will@...nel.org>,
	Waiman Long <longman@...hat.com>,
	Boqun Feng <boqun.feng@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH] locking/percpu-rwsem: do not do lock handoff in percpu_up_write

On Mon, 29 Jan 2024 12:36:20 -0800 Benjamin Segall <bsegall@...gle.com>
> 
> The basic locking issue was due to userspace rapidly spawning threads
> (or processes) more rapidly than the cpus they are running on can
> support, and this causing issues for unrelated threads doing cgroup
> operations on other cpus.
> 
> The contention can be due to a combination of just straight up spawning
> way too many, userspace misconfiguration of cpus allowed, or load
> balancer weaknesses. (If you pick minimum cpu.shares values and have
> large machines, SCHED_LOAD_RESOLUTION isn't really enough for load
> balance to do a good job, and what you're telling the load balancer you
> want isn't really a good idea in the first place).

Sigh, add change to percpu-rwsem's handoff because cgroup has a cough
in chest.