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Message-ID: <8fada9f2-7aca-44e7-adc9-3d0e7a363baf@arm.com>
Date: Thu, 6 Nov 2025 17:43:20 +0000
From: Ben Horgan <ben.horgan@....com>
To: Jonathan Cameron <jonathan.cameron@...wei.com>,
James Morse <james.morse@....com>
Cc: linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
linux-acpi@...r.kernel.org,
D Scott Phillips OS <scott@...amperecomputing.com>,
carl@...amperecomputing.com, lcherian@...vell.com,
bobo.shaobowang@...wei.com, tan.shaopeng@...itsu.com,
baolin.wang@...ux.alibaba.com, Jamie Iles <quic_jiles@...cinc.com>,
Xin Hao <xhao@...ux.alibaba.com>, peternewman@...gle.com,
dfustini@...libre.com, amitsinght@...vell.com,
David Hildenbrand <david@...hat.com>, Dave Martin <dave.martin@....com>,
Koba Ko <kobak@...dia.com>, Shanker Donthineni <sdonthineni@...dia.com>,
fenghuay@...dia.com, baisheng.gao@...soc.com, Rob Herring <robh@...nel.org>,
Rohit Mathew <rohit.mathew@....com>, Rafael Wysocki <rafael@...nel.org>,
Len Brown <lenb@...nel.org>, Lorenzo Pieralisi <lpieralisi@...nel.org>,
Hanjun Guo <guohanjun@...wei.com>, Sudeep Holla <sudeep.holla@....com>,
Catalin Marinas <catalin.marinas@....com>, Will Deacon <will@...nel.org>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Danilo Krummrich <dakr@...nel.org>, Jeremy Linton <jeremy.linton@....com>,
Gavin Shan <gshan@...hat.com>
Subject: Re: [PATCH v3 08/29] arm_mpam: Add the class and component structures
for firmware described ris
Hi Jonathan,
On 10/24/25 17:47, Jonathan Cameron wrote:
> n Fri, 17 Oct 2025 18:56:24 +0000
> James Morse <james.morse@....com> wrote:
>
>> An MSC is a container of resources, each identified by their RIS index.
>> Some RIS are described by firmware to provide their position in the system.
>> Others are discovered when the driver probes the hardware.
>>
>> To configure a resource it needs to be found by its class, e.g. 'L2'.
>> There are two kinds of grouping, a class is a set of components, which
>> are visible to user-space as there are likely to be multiple instances
>> of the L2 cache. (e.g. one per cluster or package)
>>
>> Add support for creating and destroying structures to allow a hierarchy
>> of resources to be created.
>>
>> CC: Ben Horgan <ben.horgan@....com>
>> Tested-by: Fenghua Yu <fenghuay@...dia.com>
>> Signed-off-by: James Morse <james.morse@....com>
> A few minor things inline. Mostly code ordering related to make
> it easier to review!
>
>> ---
>> drivers/resctrl/mpam_devices.c | 390 +++++++++++++++++++++++++++++++-
>> drivers/resctrl/mpam_internal.h | 93 ++++++++
>> include/linux/arm_mpam.h | 8 +-
>> 3 files changed, 483 insertions(+), 8 deletions(-)
>>
>> diff --git a/drivers/resctrl/mpam_devices.c b/drivers/resctrl/mpam_devices.c
>> index d18eeec95f79..8685e50f08c6 100644
>> --- a/drivers/resctrl/mpam_devices.c
>> +++ b/drivers/resctrl/mpam_devices.c
>> @@ -30,7 +30,7 @@
>> static DEFINE_MUTEX(mpam_list_lock);
>> static LIST_HEAD(mpam_all_msc);
>>
>> -static struct srcu_struct mpam_srcu;
>> +struct srcu_struct mpam_srcu;
>
> Meh. Others may be fussier about this but I'd rather you just
> added the extern when this was first introduced and didn't
> have this churn here.
I've dropped the static earlier now.
>
>
>> +static void mpam_vmsc_destroy(struct mpam_vmsc *vmsc)
>> +{
>> + struct mpam_component *comp = vmsc->comp;
>> +
>> + lockdep_assert_held(&mpam_list_lock);
>> +
>> + list_del_rcu(&vmsc->comp_list);
>> + add_to_garbage(vmsc);
>> +
>> + if (list_empty(&comp->vmsc))
>> + mpam_comp_destroy(comp);
>> +}
>> +
>> +static void mpam_ris_destroy(struct mpam_msc_ris *ris)
> I'd rather see the create / destroy next to each other if possible.
> Makes it easier to check this unwinds the creat path.
I've done this.
>
>> +{
>> + struct mpam_vmsc *vmsc = ris->vmsc;
>> + struct mpam_msc *msc = vmsc->msc;
>> + struct mpam_component *comp = vmsc->comp;
>> + struct mpam_class *class = comp->class;
>> +
>> + lockdep_assert_held(&mpam_list_lock);
>> +
>> + /*
>> + * It is assumed affinities don't overlap. If they do the class becomes
>> + * unusable immediately.
>> + */
>> + cpumask_andnot(&comp->affinity, &comp->affinity, &ris->affinity);
>> + cpumask_andnot(&class->affinity, &class->affinity, &ris->affinity);
>> + clear_bit(ris->ris_idx, &msc->ris_idxs);
>> + list_del_rcu(&ris->vmsc_list);
>> + list_del_rcu(&ris->msc_list);
> Can you reorder these so that they are reverse of what happens in create path?
> Makes not real difference other than slightly easier to check everything is done.
> Right now I'm failing to spot where this was added to ris->msc_list in the
> create path.
Yes, it is cleaner like that.
>
>
>> + add_to_garbage(ris);
>> +
>> + if (list_empty(&vmsc->ris))
>> + mpam_vmsc_destroy(vmsc);
>> +}
>> +
>
>> +
>> +/*
>> + * The cacheinfo structures are only populated when CPUs are online.
>> + * This helper walks the device tree to include offline CPUs too.
>
> Comment stale? It does walk a tree of devices but I'm not sure that's
> what people will read device tree as meaning.
Dropped.
>
>> + */
>> +int mpam_get_cpumask_from_cache_id(unsigned long cache_id, u32 cache_level,
>> + cpumask_t *affinity)
>> +{
>> + return acpi_pptt_get_cpumask_from_cache_id(cache_id, affinity);
>> +}
>
>> +
>> +static int mpam_ris_create_locked(struct mpam_msc *msc, u8 ris_idx,
>> + enum mpam_class_types type, u8 class_id,
>> + int component_id)
>> +{
> ...
>
>> + ris = devm_kzalloc(&msc->pdev->dev, sizeof(*ris), GFP_KERNEL);
>> + if (!ris)
>> + return -ENOMEM;
>> + init_garbage(&ris->garbage);
>> + ris->garbage.pdev = pdev;
> I wonder if it's cleaner to just pass the pdev (sometimes null) in
> as a parameter to init_garbage()
Maybe... but I've left it as is for now.
>> +
>> + class = mpam_class_find(class_id, type);
>> + if (IS_ERR(class))
>> + return PTR_ERR(class);
>
>
>
>> diff --git a/drivers/resctrl/mpam_internal.h b/drivers/resctrl/mpam_internal.h
>> index 6ac75f3613c3..1a5d96660382 100644
>> --- a/drivers/resctrl/mpam_internal.h
>> +++ b/drivers/resctrl/mpam_internal.h
>
>> +/*
>> + * Structures protected by SRCU may not be freed for a surprising amount of
>> + * time (especially if perf is running). To ensure the MPAM error interrupt can
>> + * tear down all the structures, build a list of objects that can be gargbage
>
> Spell check. garbage
Ack.
>
>> + * collected once synchronize_srcu() has returned.
>> + * If pdev is non-NULL, use devm_kfree().
>> + */
>> +struct mpam_garbage {
>> + /* member of mpam_garbage */
>> + struct llist_node llist;
>> +
>> + void *to_free;
>> + struct platform_device *pdev;
>> +};
>
Thanks,
Ben
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