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From:   "Rafael J. Wysocki" <rafael@kernel.org>
Date:   Wed, 29 Mar 2023 14:08:30 +0200
Message-ID: <CAJZ5v0iUg+BBfTkXfkc5X2SFm1icekYOU2Ow+5_4riJjs1v43A@mail.gmail.com>
Subject: Re: [PATCH v3 13/24] thermal: intel: hfi: Store per-CPU IPCC scores
To:     Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
Cc:     "Rafael J. Wysocki" <rafael@kernel.org>,
        "Peter Zijlstra (Intel)" <peterz@infradead.org>,
        Juri Lelli <juri.lelli@redhat.com>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        Ricardo Neri <ricardo.neri@intel.com>,
        "Ravi V. Shankar" <ravi.v.shankar@intel.com>,
        Ben Segall <bsegall@google.com>,
        Daniel Bristot de Oliveira <bristot@redhat.com>,
        Dietmar Eggemann <dietmar.eggemann@arm.com>,
        Len Brown <len.brown@intel.com>, Mel Gorman <mgorman@suse.de>,
        "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>,
        Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Tim Chen <tim.c.chen@linux.intel.com>,
        Valentin Schneider <vschneid@redhat.com>,
        Lukasz Luba <lukasz.luba@arm.com>,
        Ionela Voinescu <ionela.voinescu@arm.com>, x86@kernel.org,
        "Joel Fernandes (Google)" <joel@joelfernandes.org>,
        linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org,
        "Tim C . Chen" <tim.c.chen@intel.com>
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On Wed, Mar 29, 2023 at 1:32 AM Ricardo Neri
<ricardo.neri-calderon@linux.intel.com> wrote:
>
> On Mon, Mar 27, 2023 at 06:37:32PM +0200, Rafael J. Wysocki wrote:
> > On Tue, Feb 7, 2023 at 6:02 AM Ricardo Neri
> > <ricardo.neri-calderon@linux.intel.com> wrote:
> > >
> > > The scheduler reads the IPCC scores when balancing load. These reads can
> > > be quite frequent. Hardware can also update the HFI table frequently.
> > > Concurrent access may cause a lot of lock contention. It gets worse as the
> > > number of CPUs increases.
> > >
> > > Instead, create separate per-CPU IPCC scores that the scheduler can read
> > > without the HFI table lock.
> > >
> > > Cc: Ben Segall <bsegall@google.com>
> > > Cc: Daniel Bristot de Oliveira <bristot@redhat.com>
> > > Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
> > > Cc: Ionela Voinescu <ionela.voinescu@arm.com>
> > > Cc: Joel Fernandes (Google) <joel@joelfernandes.org>
> > > Cc: Len Brown <len.brown@intel.com>
> > > Cc: Lukasz Luba <lukasz.luba@arm.com>
> > > Cc: Mel Gorman <mgorman@suse.de>
> > > Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> > > Cc: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
> > > Cc: Steven Rostedt <rostedt@goodmis.org>
> > > Cc: Tim C. Chen <tim.c.chen@intel.com>
> > > Cc: Valentin Schneider <vschneid@redhat.com>
> > > Cc: x86@kernel.org
> > > Cc: linux-pm@vger.kernel.org
> > > Cc: linux-kernel@vger.kernel.org
> > > Suggested-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> > > Signed-off-by: Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
> > > ---
> > > Changes since v2:
> > >  * Only create these per-CPU variables when Intel Thread Director is
> > >    supported.
> > >
> > > Changes since v1:
> > >  * Added this patch.
> > > ---
> > >  drivers/thermal/intel/intel_hfi.c | 46 +++++++++++++++++++++++++++++++
> > >  1 file changed, 46 insertions(+)
> > >
> > > diff --git a/drivers/thermal/intel/intel_hfi.c b/drivers/thermal/intel/intel_hfi.c
> > > index 2527ae3836c7..b06021828892 100644
> > > --- a/drivers/thermal/intel/intel_hfi.c
> > > +++ b/drivers/thermal/intel/intel_hfi.c
> > > @@ -29,6 +29,7 @@
> > >  #include <linux/kernel.h>
> > >  #include <linux/math.h>
> > >  #include <linux/mutex.h>
> > > +#include <linux/percpu.h>
> > >  #include <linux/percpu-defs.h>
> > >  #include <linux/printk.h>
> > >  #include <linux/processor.h>
> > > @@ -170,6 +171,43 @@ static struct workqueue_struct *hfi_updates_wq;
> > >  #define HFI_UPDATE_INTERVAL            HZ
> > >  #define HFI_MAX_THERM_NOTIFY_COUNT     16
> > >
> > > +#ifdef CONFIG_IPC_CLASSES
> >
> > It would be good to provide a (concise) description of this variable.
> >
> > > +static int __percpu *hfi_ipcc_scores;
>
> Do you mean hfi_ipcc_scores or CONFIG_IPC_CLASSES?

hfi_ipcc_scores (as the latter is not a variable).