linux-kernel - Re: [PATCH] x86/cpu: use smp_call_function_many() in arch_freq_prepare

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Message-ID: <87bkxnnzkj.ffs@tglx>
Date:   Wed, 30 Mar 2022 19:02:36 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Eric Dumazet <edumazet@...gle.com>
Cc:     Eric Dumazet <eric.dumazet@...il.com>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        the arch/x86 maintainers <x86@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH] x86/cpu: use smp_call_function_many() in
 arch_freq_prepare_all()

On Wed, Mar 30 2022 at 09:51, Eric Dumazet wrote:
> On Wed, Mar 30, 2022 at 8:58 AM Thomas Gleixner <tglx@...utronix.de> wrote:
>> which I hate with a passion because that allows *unpriviledged* user
>> space to inject systemwide IPIs every 10ms just to read these counters
>> which are providing not more than some estimate and are of no value for
>> the only sane use case of /proc/cpuinfo, i.e. #1 above.
>
> You do realize that before my patch, this is already happening ?
>
> My "optimization" simply replace an open loop of individual IPI with
> use of the broadcast IPI capability.
>
> Are you saying we should remove IPI broadcast and use loops
> of IPI, one cpu at a time ?

I rather have no IPIs at all...