linux-kernel - Re: [PATCH 1/8] perf/x86/uncore: Save the unit control address of all units

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Date: Mon, 10 Jun 2024 15:40:59 -0700
From: Tim Chen <tim.c.chen@...ux.intel.com>
To: kan.liang@...ux.intel.com, peterz@...radead.org, mingo@...nel.org, 
	linux-kernel@...r.kernel.org
Cc: acme@...nel.org, namhyung@...nel.org, irogers@...gle.com,
 eranian@...gle.com,  ak@...ux.intel.com, yunying.sun@...el.com
Subject: Re: [PATCH 1/8] perf/x86/uncore: Save the unit control address of
 all units

On Mon, 2024-06-10 at 13:16 -0700, kan.liang@...ux.intel.com wrote:
> From: Kan Liang <kan.liang@...ux.intel.com>
> 
> The unit control address of some CXL units may be wrongly calculated
> under some configuration on a EMR machine.
> 
> The current implementation only saves the unit control address of the
> units from the first die, and the first unit of the rest of dies. Perf
> assumed that the units from the other dies have the same offset as the
> first die. So the unit control address of the rest of the units can be
> calculated. However, the assumption is wrong, especially for the CXL
> units.
> 
> Introduce an RB tree for each uncore type to save the unit control
> address and ID information for all the units.
> 
> Compared with the current implementation, more space is required to save
> the information of all units. The extra size should be acceptable.
> For example, on EMR, there are 221 units at most. For a 2-socket machine,
> the extra space is ~6KB at most.
> 
> Tested-by: Yunying Sun <yunying.sun@...el.com>
> Signed-off-by: Kan Liang <kan.liang@...ux.intel.com>
> ---
>  arch/x86/events/intel/uncore_discovery.c | 79 +++++++++++++++++++++++-
>  arch/x86/events/intel/uncore_discovery.h | 10 +++
>  2 files changed, 87 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/events/intel/uncore_discovery.c b/arch/x86/events/intel/uncore_discovery.c
> index 9a698a92962a..ce520e69a3c1 100644
> --- a/arch/x86/events/intel/uncore_discovery.c
> +++ b/arch/x86/events/intel/uncore_discovery.c
> @@ -93,6 +93,8 @@ add_uncore_discovery_type(struct uncore_unit_discovery *unit)
>  	if (!type->box_ctrl_die)
>  		goto free_type;
>  
> +	type->units = RB_ROOT;
> +
>  	type->access_type = unit->access_type;
>  	num_discovered_types[type->access_type]++;
>  	type->type = unit->box_type;
> @@ -120,10 +122,59 @@ get_uncore_discovery_type(struct uncore_unit_discovery *unit)
>  	return add_uncore_discovery_type(unit);
>  }
>  
> +static inline bool unit_less(struct rb_node *a, const struct rb_node *b)
> +{
> +	struct intel_uncore_discovery_unit *a_node, *b_node;
> +
> +	a_node = rb_entry(a, struct intel_uncore_discovery_unit, node);
> +	b_node = rb_entry(b, struct intel_uncore_discovery_unit, node);
> +
> +	if (a_node->pmu_idx < b_node->pmu_idx)
> +		return true;
> +	if (a_node->pmu_idx > b_node->pmu_idx)
> +		return false;
> +
> +	if (a_node->die < b_node->die)
> +		return true;
> +	if (a_node->die > b_node->die)
> +		return false;
> +
> +	return 0;

Will it be better if the rb_node is sorted by id instead
of pmu_idx+die? 

Then it will be faster for uncore_find_unit() to run in
O(log(N)) instead of O(N).  Right now it looks like we
are traversing the whole tree to find the entry with the
id.

Tim

> +}
> +
> +static inline struct intel_uncore_discovery_unit *
> +uncore_find_unit(struct rb_root *root, unsigned int id)
> +{
> +	struct intel_uncore_discovery_unit *unit;
> +	struct rb_node *node;
> +
> +	for (node = rb_first(root); node; node = rb_next(node)) {
> +		unit = rb_entry(node, struct intel_uncore_discovery_unit, node);
> +		if (unit->id == id)
> +			return unit;
> +	}
> +
> +	return NULL;
> +}
> +