Messages in this thread | | | Date | Tue, 28 Mar 2023 16:43:15 -0700 | From | Ricardo Neri <> | Subject | Re: [PATCH v3 13/24] thermal: intel: hfi: Store per-CPU IPCC scores |
| |
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?
> > + > > +static int alloc_hfi_ipcc_scores(void) > > +{ > > + if (!cpu_feature_enabled(X86_FEATURE_ITD)) > > + return 0; > > + > > + hfi_ipcc_scores = __alloc_percpu(sizeof(*hfi_ipcc_scores) * > > + hfi_features.nr_classes, > > + sizeof(*hfi_ipcc_scores)); > > + > > + return !hfi_ipcc_scores; > > I would do > > if (!hfi_ipcc_scores) > return -ENOMEM; > > return 0; > > Or make the function return bool.
Sure, I can make this function return -ENOMEM.
> > > +} > > + > > +static void set_hfi_ipcc_score(void *caps, int cpu) > > +{ > > + int i, *hfi_class; > > + > > + if (!cpu_feature_enabled(X86_FEATURE_ITD)) > > + return; > > + > > + hfi_class = per_cpu_ptr(hfi_ipcc_scores, cpu); > > + > > + for (i = 0; i < hfi_features.nr_classes; i++) { > > + struct hfi_cpu_data *class_caps; > > + > > + class_caps = caps + i * hfi_features.class_stride; > > + WRITE_ONCE(hfi_class[i], class_caps->perf_cap); > > As it stands, it is unclear why WRITE_ONCE() is needed here.
The CPU handling the HFI interrupt will update all the per-CPU IPCC scores. My intention is to ensure that a WRITE of a given IPCC score is completed before another CPU READs an IPCC score. The corresponding READ_ONCE happens in patch 15.
| |