linux-kernel - Re: [PATCH v3 13/24] thermal: intel: hfi: Store per-CPU IPCC scores

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Date:   Wed, 29 Mar 2023 19:15:54 -0700
From:   Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Ricardo Neri <ricardo.neri@...el.com>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        Ben Segall <bsegall@...gle.com>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Len Brown <len.brown@...el.com>, Mel Gorman <mgorman@...e.de>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Valentin Schneider <vschneid@...hat.com>,
        Lukasz Luba <lukasz.luba@....com>,
        Ionela Voinescu <ionela.voinescu@....com>, x86@...nel.org,
        "Joel Fernandes (Google)" <joel@...lfernandes.org>,
        linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        "Tim C . Chen" <tim.c.chen@...el.com>
Subject: Re: [PATCH v3 13/24] thermal: intel: hfi: Store per-CPU IPCC scores

On Wed, Mar 29, 2023 at 02:08:30PM +0200, Rafael J. Wysocki wrote:
> On Wed, Mar 29, 2023 at 1:32 AM Ricardo Neri
> <ricardo.neri-calderon@...ux.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@...ux.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@...gle.com>
> > > > Cc: Daniel Bristot de Oliveira <bristot@...hat.com>
> > > > Cc: Dietmar Eggemann <dietmar.eggemann@....com>
> > > > Cc: Ionela Voinescu <ionela.voinescu@....com>
> > > > Cc: Joel Fernandes (Google) <joel@...lfernandes.org>
> > > > Cc: Len Brown <len.brown@...el.com>
> > > > Cc: Lukasz Luba <lukasz.luba@....com>
> > > > Cc: Mel Gorman <mgorman@...e.de>
> > > > Cc: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> > > > Cc: Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
> > > > Cc: Steven Rostedt <rostedt@...dmis.org>
> > > > Cc: Tim C. Chen <tim.c.chen@...el.com>
> > > > Cc: Valentin Schneider <vschneid@...hat.com>
> > > > Cc: x86@...nel.org
> > > > Cc: linux-pm@...r.kernel.org
> > > > Cc: linux-kernel@...r.kernel.org
> > > > Suggested-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> > > > Signed-off-by: Ricardo Neri <ricardo.neri-calderon@...ux.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).

I thought so. Thank you for clarifying.