linux-kernel - Re: [PATCH v8 3/7] x86/resctrl: Refactor mbm

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Message-ID: <2ed76893-ac65-d9a2-aeea-c927ebd2a1e8@intel.com>
Date: Fri, 1 Nov 2024 15:08:27 -0700
From: Fenghua Yu <fenghua.yu@...el.com>
To: Tony Luck <tony.luck@...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: James Morse <james.morse@....com>, Jamie Iles <quic_jiles@...cinc.com>,
	Babu Moger <babu.moger@....com>, Randy Dunlap <rdunlap@...radead.org>,
	"Shaopeng Tan (Fujitsu)" <tan.shaopeng@...itsu.com>,
	<linux-kernel@...r.kernel.org>, <linux-doc@...r.kernel.org>,
	<patches@...ts.linux.dev>
Subject: Re: [PATCH v8 3/7] x86/resctrl: Refactor mbm_update()

Hi, Tony,

On 10/29/24 10:28, Tony Luck wrote:
> Computing memory bandwidth for all enabled events resulted in
> identical code blocks for total and local bandwidth in mbm_update().
> 
> Refactor with a helper function to eliminate code duplication.
> 
> No functional change.
> 
> Signed-off-by: Tony Luck <tony.luck@...el.com>
> ---
>   arch/x86/kernel/cpu/resctrl/monitor.c | 69 ++++++++++-----------------
>   1 file changed, 24 insertions(+), 45 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
> index 3ef339e405c2..1b6cb3bbc008 100644
> --- a/arch/x86/kernel/cpu/resctrl/monitor.c
> +++ b/arch/x86/kernel/cpu/resctrl/monitor.c
> @@ -829,62 +829,41 @@ static void update_mba_bw(struct rdtgroup *rgrp, struct rdt_mon_domain *dom_mbm)
>   	resctrl_arch_update_one(r_mba, dom_mba, closid, CDP_NONE, new_msr_val);
>   }
>   
> -static void mbm_update(struct rdt_resource *r, struct rdt_mon_domain *d,
> -		       u32 closid, u32 rmid)
> +static void mbm_update_one_event(struct rdt_resource *r, struct rdt_mon_domain *d,
> +				 u32 closid, u32 rmid, enum resctrl_event_id evtid)
>   {
>   	struct rmid_read rr = {0};
>   
>   	rr.r = r;
>   	rr.d = d;
> +	rr.evtid = evtid;
> +	rr.arch_mon_ctx = resctrl_arch_mon_ctx_alloc(rr.r, rr.evtid);
> +	if (IS_ERR(rr.arch_mon_ctx)) {
> +		pr_warn_ratelimited("Failed to allocate monitor context: %ld",
> +				    PTR_ERR(rr.arch_mon_ctx));
> +		return;
> +	}
> +
> +	__mon_event_count(closid, rmid, &rr);
> +

The comment (added in patch 2 and legacy code) is removed completely here.

Maybe it's better to remain the comment here?

> +	if (is_mba_sc(NULL))
> +		mbm_bw_count(closid, rmid, &rr);
> +
> +	resctrl_arch_mon_ctx_free(rr.r, rr.evtid, rr.arch_mon_ctx);
> +}
>   
> +static void mbm_update(struct rdt_resource *r, struct rdt_mon_domain *d,
> +		       u32 closid, u32 rmid)
> +{
>   	/*
>   	 * This is protected from concurrent reads from user
>   	 * as both the user and we hold the global mutex.
>   	 */
> -	if (is_mbm_total_enabled()) {
> -		rr.evtid = QOS_L3_MBM_TOTAL_EVENT_ID;
> -		rr.val = 0;
> -		rr.arch_mon_ctx = resctrl_arch_mon_ctx_alloc(rr.r, rr.evtid);
> -		if (IS_ERR(rr.arch_mon_ctx)) {
> -			pr_warn_ratelimited("Failed to allocate monitor context: %ld",
> -					    PTR_ERR(rr.arch_mon_ctx));
> -			return;
> -		}
> -
> -		__mon_event_count(closid, rmid, &rr);
> -
> -		/*
> -		 * Call the MBA software controller only for the
> -		 * control groups and when user has enabled
> -		 * the software controller explicitly.
> -		 */

Same comment was added in patch 2 but is removed in the helper. Maybe 
it's better to add back the comment in the helper.

> -		if (is_mba_sc(NULL))
> -			mbm_bw_count(closid, rmid, &rr);
> -
> -		resctrl_arch_mon_ctx_free(rr.r, rr.evtid, rr.arch_mon_ctx);
> -	}
> -	if (is_mbm_local_enabled()) {
> -		rr.evtid = QOS_L3_MBM_LOCAL_EVENT_ID;
> -		rr.val = 0;
> -		rr.arch_mon_ctx = resctrl_arch_mon_ctx_alloc(rr.r, rr.evtid);
> -		if (IS_ERR(rr.arch_mon_ctx)) {
> -			pr_warn_ratelimited("Failed to allocate monitor context: %ld",
> -					    PTR_ERR(rr.arch_mon_ctx));
> -			return;
> -		}
> -
> -		__mon_event_count(closid, rmid, &rr);
> -
> -		/*
> -		 * Call the MBA software controller only for the
> -		 * control groups and when user has enabled
> -		 * the software controller explicitly.
> -		 */

This same comment is in legacy code and is removed in the helper.

> -		if (is_mba_sc(NULL))
> -			mbm_bw_count(closid, rmid, &rr);
> +	if (is_mbm_total_enabled())
> +		mbm_update_one_event(r, d, closid, rmid, QOS_L3_MBM_TOTAL_EVENT_ID);
>   
> -		resctrl_arch_mon_ctx_free(rr.r, rr.evtid, rr.arch_mon_ctx);
> -	}
> +	if (is_mbm_local_enabled())
> +		mbm_update_one_event(r, d, closid, rmid, QOS_L3_MBM_LOCAL_EVENT_ID);
>   }
>   
>   /*

Thanks.

-Fenghua