linux-kernel - Re: [PATCH 02/27] sched/isolation: Introduce housekeeping per-cpu rwsem

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <aFmXAjmtasot2rp6@slm.duckdns.org>
Date: Mon, 23 Jun 2025 08:03:46 -1000
From: Tejun Heo <tj@...nel.org>
To: Waiman Long <llong@...hat.com>
Cc: Frederic Weisbecker <frederic@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...hat.com>,
	Marco Crivellari <marco.crivellari@...e.com>,
	Michal Hocko <mhocko@...e.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Vlastimil Babka <vbabka@...e.cz>
Subject: Re: [PATCH 02/27] sched/isolation: Introduce housekeeping per-cpu
 rwsem

Hello,

On Mon, Jun 23, 2025 at 01:57:17PM -0400, Waiman Long wrote:
> The percpu-rwsem does have a cheaper read side compared with rwsem for
> typical use case where writer update happens sparingly. However, when the
> writer has successful acquired the write lock, the readers do have to wait
> until the writer issues a percpu_up_write() call before they can proceed. It
> is the delay introduced by this wait that I am worry about. Isolated
> partitions are typically set up to run RT applications that have a strict
> latency requirement. So any possible latency spike should be avoided.

I see. Hmm... this being the mechanism that establishes the isolation, it
doesn't seem too broken if things stutter a bit when isolation is being
updated. Let's see what Frederic says why the strong interlocking is needed.

Thanks.

-- 
tejun