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From:   Peter Newman <peternewman@google.com>
Date:   Thu, 1 Jun 2023 16:45:27 +0200
Message-ID: <CALPaoChcra+qJd9ETQT+nZ17ahH0RCCarjuT3jn8EyzV2HyCbw@mail.gmail.com>
Subject: Re: [PATCH v1 3/9] x86/resctrl: Add resctrl_mbm_flush_cpu() to
 collect CPUs' MBM events
To:     Reinette Chatre <reinette.chatre@intel.com>
Cc:     Fenghua Yu <fenghua.yu@intel.com>, Babu Moger <babu.moger@amd.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>, x86@kernel.org,
        "H. Peter Anvin" <hpa@zytor.com>,
        Stephane Eranian <eranian@google.com>,
        James Morse <james.morse@arm.com>,
        linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org
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Hi Reinette,

On Thu, May 11, 2023 at 11:37=E2=80=AFPM Reinette Chatre
<reinette.chatre@intel.com> wrote:
> On 4/21/2023 7:17 AM, Peter Newman wrote:
> > +     /* Count bandwidth after the first successful counter read. */
> > +     if (counter->initialized) {
> > +             /* Assume that mbm_update() will prevent double-overflows=
. */
> > +             if (val !=3D counter->prev_bytes)
> > +                     atomic64_add(val - counter->prev_bytes,
> > +                                  &m->soft_rmid_bytes);
> > +     } else {
> > +             counter->initialized =3D true;
> > +     }
> > +
> > +     counter->prev_bytes =3D val;
>
> I notice a lot of similarities between the above and the software control=
ler,
> see mbm_bw_count().

I see the "a=3Dnow(); a-b; b=3Da;" and the not handling overflow parts
being similar, but the use of the initialized flag seems quite
different from delta_comp.

Also mbm_state is on the arch-independent side and the new code is
going to the arch-dependent side, so it wouldn't be convenient to try
to use the mbm_bw structures for this.

From this, I don't think trying to reuse this is worth it unless you
have other suggestions.

-Peter