linux-kernel - Re: [PATCH v3 02/19] x86/resctrl: Access per-rmid structures by index

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Message-ID: <3b82b55e-0fcf-1fb9-1c07-6b2cb95f6160@intel.com>
Date:   Fri, 31 Mar 2023 16:19:48 -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>
Subject: Re: [PATCH v3 02/19] x86/resctrl: Access per-rmid structures by index

Hi James,

On 3/20/2023 10:26 AM, James Morse wrote:
> Because of the differences between Intel RDT/AMD QoS and Arm's MPAM
> monitors, RMID values on arm64 are not unique unless the CLOSID is
> also included. Bitmaps like rmid_busy_llc need to be sized by the
> number of unique entries for this resource.
> 
> Add helpers to encode/decode the CLOSID and RMID to an index. The
> domain's rmid_busy__llc and the rmid_ptrs[] array are then sized by

rmid_busy__llc -> rmid_busy_llc

Not a big deal but since you are using [] for rmid_ptrs[] it should
not be necessary to say that it is an array.

> index, as are the domain mbm_local and mbm_total arrays.
> On x86, the index is always just the RMID, so all these structures
> remain the same size.
> 
> The index gives resctrl a unique value it can use to store monitor
> values, and allows MPAM to decode the closid when reading the hardware
> counters.

When you are switching between CLOSID and closid in the same context it
is less obvious that it means the same thing.

> 
> Tested-by: Shaopeng Tan <tan.shaopeng@...itsu.com>
> Signed-off-by: James Morse <james.morse@....com>
> ---
> Changes since v1:
>  * Added X86_BAD_CLOSID macro to make it clear what this value means
>  * Added second WARN_ON() for closid checking, and made both _ONCE()
> 
> Changes since v2:
>  * Added RESCTRL_RESERVED_CLOSID
>  * Removed a newline
>  * Repharsed some comments
>  * Renamed a variable 'ignore'd
>  * Moved X86_RESCTRL_BAD_CLOSID to a previous patch
> ---
>  arch/x86/include/asm/resctrl.h         | 17 ++++++
>  arch/x86/kernel/cpu/resctrl/core.c     |  2 +-
>  arch/x86/kernel/cpu/resctrl/internal.h |  1 +
>  arch/x86/kernel/cpu/resctrl/monitor.c  | 83 +++++++++++++++++---------
>  arch/x86/kernel/cpu/resctrl/rdtgroup.c |  7 ++-
>  include/linux/resctrl.h                |  3 +
>  6 files changed, 82 insertions(+), 31 deletions(-)
> 
> diff --git a/arch/x86/include/asm/resctrl.h b/arch/x86/include/asm/resctrl.h
> index cbe986d23df6..3ca40be41a0a 100644
> --- a/arch/x86/include/asm/resctrl.h
> +++ b/arch/x86/include/asm/resctrl.h
> @@ -101,6 +101,23 @@ static inline void resctrl_sched_in(void)
>  		__resctrl_sched_in();
>  }
>  
> +static inline u32 resctrl_arch_system_num_rmid_idx(void)
> +{
> +	/* RMID are independent numbers for x86. num_rmid_idx==num_rmid */

Could you add spaces around the "=="?

> +	return boot_cpu_data.x86_cache_max_rmid + 1;
> +}
> +
> +static inline void resctrl_arch_rmid_idx_decode(u32 idx, u32 *closid, u32 *rmid)
> +{
> +	*rmid = idx;
> +	*closid = X86_RESCTRL_BAD_CLOSID;
> +}
> +
> +static inline u32 resctrl_arch_rmid_idx_encode(u32 ignored, u32 rmid)
> +{
> +	return rmid;
> +}
> +
>  void resctrl_cpu_detect(struct cpuinfo_x86 *c);
>  
>  #else
> diff --git a/arch/x86/kernel/cpu/resctrl/core.c b/arch/x86/kernel/cpu/resctrl/core.c
> index 030d3b409768..351319403f84 100644
> --- a/arch/x86/kernel/cpu/resctrl/core.c
> +++ b/arch/x86/kernel/cpu/resctrl/core.c
> @@ -600,7 +600,7 @@ static void clear_closid_rmid(int cpu)
>  	state->default_rmid = 0;
>  	state->cur_closid = 0;
>  	state->cur_rmid = 0;
> -	wrmsr(MSR_IA32_PQR_ASSOC, 0, 0);
> +	wrmsr(MSR_IA32_PQR_ASSOC, RESCTRL_RESERVED_CLOSID, 0);
>  }
>  
>  static int resctrl_online_cpu(unsigned int cpu)
> diff --git a/arch/x86/kernel/cpu/resctrl/internal.h b/arch/x86/kernel/cpu/resctrl/internal.h
> index c64097947994..47506e2afd59 100644
> --- a/arch/x86/kernel/cpu/resctrl/internal.h
> +++ b/arch/x86/kernel/cpu/resctrl/internal.h
> @@ -7,6 +7,7 @@
>  #include <linux/kernfs.h>
>  #include <linux/fs_context.h>
>  #include <linux/jump_label.h>
> +#include <asm/resctrl.h>
>  
>  #define L3_QOS_CDP_ENABLE		0x01ULL
>  
> diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
> index 18c37d364030..03a7d13dd653 100644
> --- a/arch/x86/kernel/cpu/resctrl/monitor.c
> +++ b/arch/x86/kernel/cpu/resctrl/monitor.c
> @@ -142,12 +142,29 @@ static inline u64 get_corrected_mbm_count(u32 rmid, unsigned long val)
>  	return val;
>  }
>  
> -static inline struct rmid_entry *__rmid_entry(u32 closid, u32 rmid)
> +/*
> + * x86 and arm64 differ in their handling of monitoring.
> + * x86's RMID are an independent number, there is only one source of traffic
> + * an RMID value of '1'.

"source of traffic an RMID" -> "source of traffic with an RMID" ?

> + * arm64's PMG extend the PARTID/CLOSID space, there are multiple sources of
> + * traffic with a PMG value of '1', one for each CLOSID, meaining the RMID

meaining -> meaning

> + * value is no longer unique.

Reinette