linux-kernel - Re: [PATCH v2] x86,mm: only trim the mm

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

Message-ID: <5544716d-31be-40c6-a289-030220e518de@intel.com>
Date: Tue, 3 Dec 2024 12:05:28 -0800
From: Dave Hansen <dave.hansen@...el.com>
To: Rik van Riel <riel@...riel.com>,
 Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc: kernel test robot <oliver.sang@...el.com>, oe-lkp@...ts.linux.dev,
 lkp@...el.com, linux-kernel@...r.kernel.org, x86@...nel.org,
 Ingo Molnar <mingo@...nel.org>,
 Linus Torvalds <torvalds@...ux-foundation.org>,
 Peter Zijlstra <peterz@...radead.org>, Mel Gorman <mgorman@...e.de>
Subject: Re: [PATCH v2] x86,mm: only trim the mm_cpumask once a second

On 12/3/24 11:48, Rik van Riel wrote:
> Sending TLB flush IPIs to CPUs that are in the mm_cpumask, but no
> longer running the program causes a regression in the will-it-scale
> tlbflush2 test. This test is contrived, but a large regression here
> might cause a small regression in some real world workload.

The patch seems OK in theory, but this explanation doesn't sit right
with me.

Most of the will-it-scale tests including tlbflush2 have long-lived
CPU-bound threads. They shouldn't schedule out much at all during the
benchmark. I don't see how they could drive a significant increase in
IPIs to cause a 10%+ regression.

I'd much prefer that we understand the regression in detail before
throwing more code at fixing it.