linux-kernel - Re: [PATCH v2] watchdog: Prefer use "ref-cycles" for NMI watchdog

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: <1DEE93B2-BA74-4266-A3C1-22A9DDEB63A8@fb.com>
Date:   Wed, 17 May 2023 17:51:01 +0000
From:   Song Liu <songliubraving@...a.com>
To:     Peter Zijlstra <peterz@...radead.org>
CC:     Song Liu <song@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Kernel Team <kernel-team@...a.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v2] watchdog: Prefer use "ref-cycles" for NMI watchdog



> On May 17, 2023, at 12:31 AM, Peter Zijlstra <peterz@...radead.org> wrote:
> 
> On Tue, May 16, 2023 at 04:58:17PM -0700, Song Liu wrote:
>> NMI watchdog permanently consumes one hardware counters per CPU on the
>> system. For systems that use many hardware counters, this causes more
>> aggressive time multiplexing of perf events.
>> 
>> OTOH, some CPUs (mostly Intel) support "ref-cycles" event, which is rarely
>> used. Try use "ref-cycles" for the watchdog, so that one more hardware
>> counter is available to the user. If the CPU doesn't support "ref-cycles",
>> fall back to "cycles".
>> 
>> The downside of this change is that users of "ref-cycles" need to disable
>> nmi_watchdog.
> 
> I still utterly hate how you hardcode ref-cycles

OK.. let me try with kernel cmdline args. Sending v3. 

Thanks,
Song