linux-kernel - Re: [PATCH v4 15/24] x86/resctrl: Allow arch to allocate memory needed in resctrl_arch_rmid

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Message-ID: <c3f3ce07-3402-4cd5-fcf8-1d505ee820e7@intel.com>
Date:   Thu, 15 Jun 2023 15:13:35 -0700
From:   Reinette Chatre <reinette.chatre@...el.com>
To:     James Morse <james.morse@....com>, <x86@...nel.org>,
        <linux-kernel@...r.kernel.org>
CC:     Fenghua Yu <fenghua.yu@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        H Peter Anvin <hpa@...or.com>,
        Babu Moger <Babu.Moger@....com>,
        <shameerali.kolothum.thodi@...wei.com>,
        D Scott Phillips OS <scott@...amperecomputing.com>,
        <carl@...amperecomputing.com>, <lcherian@...vell.com>,
        <bobo.shaobowang@...wei.com>, <tan.shaopeng@...itsu.com>,
        <xingxin.hx@...nanolis.org>, <baolin.wang@...ux.alibaba.com>,
        Jamie Iles <quic_jiles@...cinc.com>,
        Xin Hao <xhao@...ux.alibaba.com>, <peternewman@...gle.com>,
        <dfustini@...libre.com>
Subject: Re: [PATCH v4 15/24] x86/resctrl: Allow arch to allocate memory
 needed in resctrl_arch_rmid_read()

Hi James,

On 5/25/2023 11:02 AM, James Morse wrote:
> Depending on the number of monitors available, Arm's MPAM may need to
> allocate a monitor prior to reading the counter value. Allocating a
> contended resource may involve sleeping.
> 
> add_rmid_to_limbo() calls resctrl_arch_rmid_read() for multiple domains,
> the allocation should be valid for all domains.
> 
> __check_limbo() and mon_event_count() each make multiple calls to
> resctrl_arch_rmid_read(), to avoid extra work on contended systems,
> the allocation should be valid for multiple invocations of
> resctrl_arch_rmid_read().
> 
> Add arch hooks for this allocation, which need calling before
> resctrl_arch_rmid_read(). The allocated monitor is passed to
> resctrl_arch_rmid_read(), then freed again afterwards. The helper
> can be called on any CPU, and can sleep.
> 
> Tested-by: Shaopeng Tan <tan.shaopeng@...itsu.com>
> Signed-off-by: James Morse <james.morse@....com>
> ----

Note the extra "-" 

> Changes since v3:
>  * Expanded comment.
>  * Removed stray header include.
>  * Reworded commit message.
>  * Made ctx a void * instead of an int.
> ---

...

> diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
> index fb33100e172b..6d140018358a 100644
> --- a/arch/x86/kernel/cpu/resctrl/monitor.c
> +++ b/arch/x86/kernel/cpu/resctrl/monitor.c
> @@ -264,7 +264,7 @@ static u64 mbm_overflow_count(u64 prev_msr, u64 cur_msr, unsigned int width)
>  
>  int resctrl_arch_rmid_read(struct rdt_resource *r, struct rdt_domain *d,
>  			   u32 closid, u32 rmid, enum resctrl_event_id eventid,
> -			   u64 *val)
> +			   u64 *val, void *ignored)
>  {
>  	struct rdt_hw_resource *hw_res = resctrl_to_arch_res(r);
>  	struct rdt_hw_domain *hw_dom = resctrl_to_arch_dom(d);
> @@ -331,9 +331,14 @@ void __check_limbo(struct rdt_domain *d, bool force_free)
>  	u32 idx_limit = resctrl_arch_system_num_rmid_idx();
>  	struct rmid_entry *entry;
>  	u32 idx, cur_idx = 1;
> +	void *arch_mon_ctx;
>  	bool rmid_dirty;
>  	u64 val = 0;
>  
> +	arch_mon_ctx = resctrl_arch_mon_ctx_alloc(r, QOS_L3_OCCUP_EVENT_ID);
> +	if (arch_mon_ctx < 0)
> +		return;
> +

It seems that not all has adapted to the new type.

>  	/*
>  	 * Skip RMID 0 and start from RMID 1 and check all the RMIDs that
>  	 * are marked as busy for occupancy < threshold. If the occupancy
> @@ -347,7 +352,8 @@ void __check_limbo(struct rdt_domain *d, bool force_free)
>  
>  		entry = __rmid_entry(idx);
>  		if (resctrl_arch_rmid_read(r, d, entry->closid, entry->rmid,
> -					   QOS_L3_OCCUP_EVENT_ID, &val)) {
> +					   QOS_L3_OCCUP_EVENT_ID, &val,
> +					   arch_mon_ctx)) {
>  			rmid_dirty = true;
>  		} else {
>  			rmid_dirty = (val >= resctrl_rmid_realloc_threshold);
> @@ -360,6 +366,8 @@ void __check_limbo(struct rdt_domain *d, bool force_free)
>  		}
>  		cur_idx = idx + 1;
>  	}
> +
> +	resctrl_arch_mon_ctx_free(r, QOS_L3_OCCUP_EVENT_ID, arch_mon_ctx);
>  }
>  
>  bool has_busy_rmid(struct rdt_resource *r, struct rdt_domain *d)
> @@ -539,7 +547,7 @@ static int __mon_event_count(u32 closid, u32 rmid, struct rmid_read *rr)
>  	}
>  
>  	rr->err = resctrl_arch_rmid_read(rr->r, rr->d, closid, rmid, rr->evtid,
> -					 &tval);
> +					 &tval, rr->arch_mon_ctx);
>  	if (rr->err)
>  		return rr->err;
>  
> @@ -589,7 +597,6 @@ void mon_event_count(void *info)
>  	int ret;
>  
>  	rdtgrp = rr->rgrp;
> -
>  	ret = __mon_event_count(rdtgrp->closid, rdtgrp->mon.rmid, rr);
>  

Stray change.

>  	/*


Reinette