Message-ID: <fd8a44a1-9001-4e3e-a1a9-63e7f737e6e1@amd.com>
Date:   Mon, 4 Dec 2023 10:24:58 -0600
From:   "Moger, Babu" <babu.moger@....com>
To:     Tony Luck <tony.luck@...el.com>, Fenghua Yu <fenghua.yu@...el.com>,
        Reinette Chatre <reinette.chatre@...el.com>,
        Peter Newman <peternewman@...gle.com>,
        Jonathan Corbet <corbet@....net>,
        Shuah Khan <skhan@...uxfoundation.org>, x86@...nel.org
Cc:     Shaopeng Tan <tan.shaopeng@...itsu.com>,
        James Morse <james.morse@....com>,
        Jamie Iles <quic_jiles@...cinc.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
        patches@...ts.linux.dev
Subject: Re: [PATCH v5] x86/resctrl: Add event choices for mba_MBps

Hi Tony,

You are intending to achieve two things at once here.
1. Adding new mount option
2. Changing behaviour for the current option.
I think you need to split this patch into two. Few comments below.

On 12/1/23 15:47, Tony Luck wrote:
> The MBA Software Controller(mba_sc) is a feedback loop that uses
> measurements of local memory bandwidth to adjust MBA throttling levels to
> keep workloads in a resctrl group within a target bandwidth set in the
> schemata file.
> 
> But on Intel systems the memory bandwidth monitoring events are
> independently enumerated. It is possible for a system to support
> total memory bandwidth monitoring, but not support local bandwidth
> monitoring. On such a system a user could not enable mba_sc mode.
> Users will see this highly unhelpful error message from mount:
> 
>  # mount -t resctrl -o mba_MBps resctrl /sys/fs/resctrl
>  mount: /sys/fs/resctrl: wrong fs type, bad option, bad superblock on
>  resctrl, missing codepage or helper program, or other error.
>  dmesg(1) may have more information after failed mount system call.
> 
> dmesg(1) does not provide any additional information.
> 
> Add a new mount option "mba_MBps_event=[local|total]" that allows
> a user to specify which monitoring event to use. Also modify the
> existing "mba_MBps" option to switch to total bandwidth monitoring
> if local monitoring is not available.

I am not sure why you need both these options. I feel you just need one of
these options.

Thanks
Babu

> 
> Update the once-per-second polling code to use the chosen event (local
> or total memory bandwidth).
> 
> Signed-off-by: Tony Luck <tony.luck@...el.com>
> ---
>  Documentation/arch/x86/resctrl.rst     |  7 +++-
>  include/linux/resctrl.h                |  2 ++
>  arch/x86/kernel/cpu/resctrl/internal.h |  3 +-
>  arch/x86/kernel/cpu/resctrl/monitor.c  | 21 ++++++-----
>  arch/x86/kernel/cpu/resctrl/rdtgroup.c | 48 ++++++++++++++++++++------
>  5 files changed, 58 insertions(+), 23 deletions(-)
> 
> diff --git a/Documentation/arch/x86/resctrl.rst b/Documentation/arch/x86/resctrl.rst
> index a6279df64a9d..f06cb189911a 100644
> --- a/Documentation/arch/x86/resctrl.rst
> +++ b/Documentation/arch/x86/resctrl.rst
> @@ -45,7 +45,12 @@ mount options are:
>  	Enable code/data prioritization in L2 cache allocations.
>  "mba_MBps":
>  	Enable the MBA Software Controller(mba_sc) to specify MBA
> -	bandwidth in MBps
> +	bandwidth in MBps. Defaults to using MBM local bandwidth,
> +	but will use total bandwidth on systems that do not support
> +	local bandwidth monitoring.
> +"mba_MBps_event=[local|total]":
> +	Enable the MBA Software Controller(mba_sc) with a specific
> +	MBM event as input to the feedback loop.
>  "debug":
>  	Make debug files accessible. Available debug files are annotated with
>  	"Available only with debug option".
> diff --git a/include/linux/resctrl.h b/include/linux/resctrl.h
> index 66942d7fba7f..1feb3b2e64fa 100644
> --- a/include/linux/resctrl.h
> +++ b/include/linux/resctrl.h
> @@ -129,6 +129,7 @@ enum membw_throttle_mode {
>   * @throttle_mode:	Bandwidth throttling mode when threads request
>   *			different memory bandwidths
>   * @mba_sc:		True if MBA software controller(mba_sc) is enabled
> + * @mba_mbps_event:	Event (local or total) for mba_sc
>   * @mb_map:		Mapping of memory B/W percentage to memory B/W delay
>   */
>  struct resctrl_membw {
> @@ -138,6 +139,7 @@ struct resctrl_membw {
>  	bool				arch_needs_linear;
>  	enum membw_throttle_mode	throttle_mode;
>  	bool				mba_sc;
> +	enum resctrl_event_id		mba_mbps_event;
>  	u32				*mb_map;
>  };
>  
> diff --git a/arch/x86/kernel/cpu/resctrl/internal.h b/arch/x86/kernel/cpu/resctrl/internal.h
> index a4f1aa15f0a2..8b9b8f664324 100644
> --- a/arch/x86/kernel/cpu/resctrl/internal.h
> +++ b/arch/x86/kernel/cpu/resctrl/internal.h
> @@ -58,7 +58,8 @@ struct rdt_fs_context {
>  	struct kernfs_fs_context	kfc;
>  	bool				enable_cdpl2;
>  	bool				enable_cdpl3;
> -	bool				enable_mba_mbps;
> +	bool				enable_mba_mbps_local;
> +	bool				enable_mba_mbps_total;
>  	bool				enable_debug;
>  };
>  
> diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
> index f136ac046851..d9e590f1cbc3 100644
> --- a/arch/x86/kernel/cpu/resctrl/monitor.c
> +++ b/arch/x86/kernel/cpu/resctrl/monitor.c
> @@ -431,9 +431,10 @@ static int __mon_event_count(u32 rmid, struct rmid_read *rr)
>   */
>  static void mbm_bw_count(u32 rmid, struct rmid_read *rr)
>  {
> -	struct mbm_state *m = &rr->d->mbm_local[rmid];
>  	u64 cur_bw, bytes, cur_bytes;
> +	struct mbm_state *m;
>  
> +	m = get_mbm_state(rr->d, rmid, rr->evtid);
>  	cur_bytes = rr->val;
>  	bytes = cur_bytes - m->prev_bw_bytes;
>  	m->prev_bw_bytes = cur_bytes;
> @@ -521,19 +522,21 @@ static void update_mba_bw(struct rdtgroup *rgrp, struct rdt_domain *dom_mbm)
>  	u32 closid, rmid, cur_msr_val, new_msr_val;
>  	struct mbm_state *pmbm_data, *cmbm_data;
>  	u32 cur_bw, delta_bw, user_bw;
> +	enum resctrl_event_id evt_id;
>  	struct rdt_resource *r_mba;
>  	struct rdt_domain *dom_mba;
>  	struct list_head *head;
>  	struct rdtgroup *entry;
>  
> -	if (!is_mbm_local_enabled())
> +	if (!is_mbm_enabled())
>  		return;
>  
>  	r_mba = &rdt_resources_all[RDT_RESOURCE_MBA].r_resctrl;
> +	evt_id = r_mba->membw.mba_mbps_event;
>  
>  	closid = rgrp->closid;
>  	rmid = rgrp->mon.rmid;
> -	pmbm_data = &dom_mbm->mbm_local[rmid];
> +	pmbm_data = get_mbm_state(dom_mbm, rmid, evt_id);
>  
>  	dom_mba = get_domain_from_cpu(smp_processor_id(), r_mba);
>  	if (!dom_mba) {
> @@ -553,7 +556,7 @@ static void update_mba_bw(struct rdtgroup *rgrp, struct rdt_domain *dom_mbm)
>  	 */
>  	head = &rgrp->mon.crdtgrp_list;
>  	list_for_each_entry(entry, head, mon.crdtgrp_list) {
> -		cmbm_data = &dom_mbm->mbm_local[entry->mon.rmid];
> +		cmbm_data = get_mbm_state(dom_mbm, entry->mon.rmid, evt_id);
>  		cur_bw += cmbm_data->prev_bw;
>  		delta_bw += cmbm_data->delta_bw;
>  	}
> @@ -616,18 +619,14 @@ static void mbm_update(struct rdt_resource *r, struct rdt_domain *d, int rmid)
>  		rr.evtid = QOS_L3_MBM_TOTAL_EVENT_ID;
>  		rr.val = 0;
>  		__mon_event_count(rmid, &rr);
> +		if (is_mba_sc(NULL) && rr.evtid == r->membw.mba_mbps_event)
> +			mbm_bw_count(rmid, &rr);
>  	}
>  	if (is_mbm_local_enabled()) {
>  		rr.evtid = QOS_L3_MBM_LOCAL_EVENT_ID;
>  		rr.val = 0;
>  		__mon_event_count(rmid, &rr);
> -
> -		/*
> -		 * Call the MBA software controller only for the
> -		 * control groups and when user has enabled
> -		 * the software controller explicitly.
> -		 */
> -		if (is_mba_sc(NULL))
> +		if (is_mba_sc(NULL) && rr.evtid == r->membw.mba_mbps_event)
>  			mbm_bw_count(rmid, &rr);
>  	}
>  }
> diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> index 69a1de92384a..79141d33d5b4 100644
> --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> @@ -2294,7 +2294,7 @@ static bool supports_mba_mbps(void)
>  {
>  	struct rdt_resource *r = &rdt_resources_all[RDT_RESOURCE_MBA].r_resctrl;
>  
> -	return (is_mbm_local_enabled() &&
> +	return (is_mbm_enabled() &&
>  		r->alloc_capable && is_mba_linear());
>  }
>  
> @@ -2302,7 +2302,7 @@ static bool supports_mba_mbps(void)
>   * Enable or disable the MBA software controller
>   * which helps user specify bandwidth in MBps.
>   */
> -static int set_mba_sc(bool mba_sc)
> +static int set_mba_sc(bool mba_sc, enum resctrl_event_id mba_mbps_event)
>  {
>  	struct rdt_resource *r = &rdt_resources_all[RDT_RESOURCE_MBA].r_resctrl;
>  	u32 num_closid = resctrl_arch_get_num_closid(r);
> @@ -2313,6 +2313,7 @@ static int set_mba_sc(bool mba_sc)
>  		return -EINVAL;
>  
>  	r->membw.mba_sc = mba_sc;
> +	r->membw.mba_mbps_event = mba_mbps_event;
>  
>  	list_for_each_entry(d, &r->domains, list) {
>  		for (i = 0; i < num_closid; i++)
> @@ -2445,13 +2446,14 @@ static void rdt_disable_ctx(void)
>  {
>  	resctrl_arch_set_cdp_enabled(RDT_RESOURCE_L3, false);
>  	resctrl_arch_set_cdp_enabled(RDT_RESOURCE_L2, false);
> -	set_mba_sc(false);
> +	set_mba_sc(false, QOS_L3_MBM_LOCAL_EVENT_ID);
>  
>  	resctrl_debug = false;
>  }
>  
>  static int rdt_enable_ctx(struct rdt_fs_context *ctx)
>  {
> +	enum resctrl_event_id mba_mbps_event;
>  	int ret = 0;
>  
>  	if (ctx->enable_cdpl2) {
> @@ -2466,8 +2468,12 @@ static int rdt_enable_ctx(struct rdt_fs_context *ctx)
>  			goto out_cdpl2;
>  	}
>  
> -	if (ctx->enable_mba_mbps) {
> -		ret = set_mba_sc(true);
> +	if (ctx->enable_mba_mbps_local || ctx->enable_mba_mbps_total) {
> +		if (ctx->enable_mba_mbps_total)
> +			mba_mbps_event = QOS_L3_MBM_TOTAL_EVENT_ID;
> +		else
> +			mba_mbps_event = QOS_L3_MBM_LOCAL_EVENT_ID;
> +		ret = set_mba_sc(true, mba_mbps_event);
>  		if (ret)
>  			goto out_cdpl3;
>  	}
> @@ -2683,15 +2689,17 @@ enum rdt_param {
>  	Opt_cdp,
>  	Opt_cdpl2,
>  	Opt_mba_mbps,
> +	Opt_mba_mbps_event,
>  	Opt_debug,
>  	nr__rdt_params
>  };
>  
>  static const struct fs_parameter_spec rdt_fs_parameters[] = {
> -	fsparam_flag("cdp",		Opt_cdp),
> -	fsparam_flag("cdpl2",		Opt_cdpl2),
> -	fsparam_flag("mba_MBps",	Opt_mba_mbps),
> -	fsparam_flag("debug",		Opt_debug),
> +	fsparam_flag("cdp",			Opt_cdp),
> +	fsparam_flag("cdpl2",			Opt_cdpl2),
> +	fsparam_flag("mba_MBps",		Opt_mba_mbps),
> +	fsparam_string("mba_MBps_event",	Opt_mba_mbps_event),
> +	fsparam_flag("debug",			Opt_debug),
>  	{}
>  };
>  
> @@ -2715,7 +2723,27 @@ static int rdt_parse_param(struct fs_context *fc, struct fs_parameter *param)
>  	case Opt_mba_mbps:
>  		if (!supports_mba_mbps())
>  			return -EINVAL;
> -		ctx->enable_mba_mbps = true;
> +		if (is_mbm_local_enabled())
> +			ctx->enable_mba_mbps_local = true;
> +		else if (is_mbm_total_enabled())
> +			ctx->enable_mba_mbps_total = true;
> +		else
> +			return -EINVAL;
> +		return 0;
> +	case Opt_mba_mbps_event:
> +		if (!supports_mba_mbps())
> +			return -EINVAL;
> +		if (!strcmp("local", param->string)) {
> +			if (!is_mbm_local_enabled())
> +				return -EINVAL;
> +			ctx->enable_mba_mbps_local = true;
> +		} else if (!strcmp("total", param->string)) {
> +			if (!is_mbm_total_enabled())
> +				return -EINVAL;
> +			ctx->enable_mba_mbps_total = true;
> +		} else {
> +			return -EINVAL;
> +		}
>  		return 0;
>  	case Opt_debug:
>  		ctx->enable_debug = true;

-- 
Thanks
Babu Moger

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