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

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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