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Message-ID: <50084b31-49e4-41c7-be1e-24773d03d5d3@intel.com>
Date: Thu, 19 Sep 2024 09:42:27 -0700
From: Reinette Chatre <reinette.chatre@...el.com>
To: Babu Moger <babu.moger@....com>, <corbet@....net>, <fenghua.yu@...el.com>,
<tglx@...utronix.de>, <mingo@...hat.com>, <bp@...en8.de>,
<dave.hansen@...ux.intel.com>
CC: <x86@...nel.org>, <hpa@...or.com>, <paulmck@...nel.org>,
<rdunlap@...radead.org>, <tj@...nel.org>, <peterz@...radead.org>,
<yanjiewtw@...il.com>, <kim.phillips@....com>, <lukas.bulwahn@...il.com>,
<seanjc@...gle.com>, <jmattson@...gle.com>, <leitao@...ian.org>,
<jpoimboe@...nel.org>, <rick.p.edgecombe@...el.com>,
<kirill.shutemov@...ux.intel.com>, <jithu.joseph@...el.com>,
<kai.huang@...el.com>, <kan.liang@...ux.intel.com>,
<daniel.sneddon@...ux.intel.com>, <pbonzini@...hat.com>,
<sandipan.das@....com>, <ilpo.jarvinen@...ux.intel.com>,
<peternewman@...gle.com>, <maciej.wieczor-retman@...el.com>,
<linux-doc@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
<eranian@...gle.com>, <james.morse@....com>
Subject: Re: [PATCH v7 09/24] x86/resctrl: Introduce bitmap mbm_cntr_free_map
to track assignable counters
Hi Babu,
On 9/4/24 3:21 PM, Babu Moger wrote:
> Hardware provides a set of counters when mbm_cntr_assignable feature is
> supported. These counters are used for assigning the events in resctrl
> a group when the feature is enabled. The kernel must manage and track the
The second sentence ("These counters ...") is difficult to parse.
> number of available counters.
"The kernel must manage and track the number of available counters." ->
"The kernel must manage and track the available counters." ?
>
> Introduce mbm_cntr_free_map bitmap to track available counters and set
> of routines to allocate and free the counters.
>
> Signed-off-by: Babu Moger <babu.moger@....com>
> ---
...
> diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
> index e3e71843401a..f98cc5b9bebc 100644
> --- a/arch/x86/kernel/cpu/resctrl/monitor.c
> +++ b/arch/x86/kernel/cpu/resctrl/monitor.c
> @@ -1175,6 +1175,30 @@ static __init int snc_get_config(void)
> return ret;
> }
>
> +/*
> + * Counter bitmap for tracking the available counters.
> + * 'mbm_cntr_assign' mode provides set of hardware counters for assigning
> + * RMID, event pair. Each RMID and event pair takes one hardware counter.
(soft-ABMC may need to edit this comment)
> + * Kernel needs to keep track of the number of available counters.
Last sentence seems to be duplicate of the first?
> + */
> +static int mbm_cntrs_init(struct rdt_resource *r)
Needs __init?
> +{
> + if (r->mon.mbm_cntr_assignable) {
> + r->mon.mbm_cntr_free_map = bitmap_zalloc(r->mon.num_mbm_cntrs,
> + GFP_KERNEL);
> + if (!r->mon.mbm_cntr_free_map)
> + return -ENOMEM;
> + bitmap_fill(r->mon.mbm_cntr_free_map, r->mon.num_mbm_cntrs);
> + }
> + return 0;
> +}
> +
> +static void __exit mbm_cntrs_exit(struct rdt_resource *r)
> +{
> + if (r->mon.mbm_cntr_assignable)
> + bitmap_free(r->mon.mbm_cntr_free_map);
> +}
> +
> int __init rdt_get_mon_l3_config(struct rdt_resource *r)
> {
> unsigned int mbm_offset = boot_cpu_data.x86_cache_mbm_width_offset;
> @@ -1240,6 +1264,10 @@ int __init rdt_get_mon_l3_config(struct rdt_resource *r)
> }
> }
>
> + ret = mbm_cntrs_init(r);
> + if (ret)
> + return ret;
Missing cleanup of earlier allocation on error path here. Even so, this does not
seem to integrate with existing dom_data_init() wrt ordering and locking. Could
this be more fitting when merged with dom_data_init() (after moving it)?
> +
> l3_mon_evt_init(r);
>
> r->mon_capable = true;
> @@ -1247,9 +1275,10 @@ int __init rdt_get_mon_l3_config(struct rdt_resource *r)
> return 0;
> }
>
> -void __exit rdt_put_mon_l3_config(void)
> +void __exit rdt_put_mon_l3_config(struct rdt_resource *r)
> {
> dom_data_exit();
> + mbm_cntrs_exit(r);
There is a mismatch wrt locking used in dom_data_exit() and mbm_cntrs_exit() that is
sure to cause confusion and difficulty in the MPAM transition.
> }
>
> void __init intel_rdt_mbm_apply_quirk(void)
> diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> index ba737890d5c2..a51992984832 100644
> --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> @@ -185,6 +185,25 @@ bool closid_allocated(unsigned int closid)
> return !test_bit(closid, &closid_free_map);
> }
>
> +int mbm_cntr_alloc(struct rdt_resource *r)
> +{
> + int cntr_id;
> +
> + cntr_id = find_first_bit(r->mon.mbm_cntr_free_map,
> + r->mon.num_mbm_cntrs);
> + if (cntr_id >= r->mon.num_mbm_cntrs)
> + return -ENOSPC;
> +
> + __clear_bit(cntr_id, r->mon.mbm_cntr_free_map);
> +
> + return cntr_id;
> +}
> +
> +void mbm_cntr_free(struct rdt_resource *r, u32 cntr_id)
> +{
> + __set_bit(cntr_id, r->mon.mbm_cntr_free_map);
> +}
> +
> /**
> * rdtgroup_mode_by_closid - Return mode of resource group with closid
> * @closid: closid if the resource group
> diff --git a/include/linux/resctrl.h b/include/linux/resctrl.h
> index f11d6fdfd977..aab22ff8e0c1 100644
> --- a/include/linux/resctrl.h
> +++ b/include/linux/resctrl.h
> @@ -187,12 +187,14 @@ enum resctrl_scope {
> * @num_rmid: Number of RMIDs available
> * @num_mbm_cntrs: Number of assignable monitoring counters
> * @mbm_cntr_assignable:Is system capable of supporting monitor assignment?
> + * @mbm_cntr_free_map: bitmap of number of assignable MBM counters
The "number of" is not clear ... it seems to indicate tracking a count? How about
just "bitmap of free MBM counters"
> * @evt_list: List of monitoring events
> */
> struct resctrl_mon {
> int num_rmid;
> int num_mbm_cntrs;
> bool mbm_cntr_assignable;
> + unsigned long *mbm_cntr_free_map;
> struct list_head evt_list;
> };
>
Reinette
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