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Message-ID: <272dc6d5-eb63-4dde-8201-880acc9a3846@intel.com>
Date: Thu, 17 Jul 2025 20:51:56 -0700
From: Reinette Chatre <reinette.chatre@...el.com>
To: Babu Moger <babu.moger@....com>, <corbet@....net>, <tony.luck@...el.com>,
<james.morse@....com>, <tglx@...utronix.de>, <mingo@...hat.com>,
<bp@...en8.de>, <dave.hansen@...ux.intel.com>
CC: <Dave.Martin@....com>, <x86@...nel.org>, <hpa@...or.com>,
<akpm@...ux-foundation.org>, <paulmck@...nel.org>, <rostedt@...dmis.org>,
<Neeraj.Upadhyay@....com>, <david@...hat.com>, <arnd@...db.de>,
<fvdl@...gle.com>, <seanjc@...gle.com>, <jpoimboe@...nel.org>,
<pawan.kumar.gupta@...ux.intel.com>, <xin@...or.com>,
<manali.shukla@....com>, <tao1.su@...ux.intel.com>, <sohil.mehta@...el.com>,
<kai.huang@...el.com>, <xiaoyao.li@...el.com>, <peterz@...radead.org>,
<xin3.li@...el.com>, <kan.liang@...ux.intel.com>,
<mario.limonciello@....com>, <thomas.lendacky@....com>, <perry.yuan@....com>,
<gautham.shenoy@....com>, <chang.seok.bae@...el.com>,
<linux-doc@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
<peternewman@...gle.com>, <eranian@...gle.com>
Subject: Re: [PATCH v15 22/34] x86/resctrl: Implement
resctrl_arch_reset_cntr() and resctrl_arch_cntr_read()
Hi Babu,
On 7/8/25 3:17 PM, Babu Moger wrote:
> System software can read resctrl event data for a particular resource by
> writing the RMID and Event Identifier (EvtID) to the QM_EVTSEL register
> and then reading the event data from the QM_CTR register.
>
> In ABMC mode, the event data of a specific counter ID can be read by
> setting the following fields in QM_EVTSEL.ExtendedEvtID = 1,
Seems easier to parse when "fields in" -> "fields:".
> QM_EVTSEL.EvtID = L3CacheABMC (=1) and setting [RMID] to the desired
> counter ID. Reading QM_CTR will then return the contents of the specified
> counter ID. The E bit will be set if the counter configuration was invalid,
Where is "the E bit" defined?
> or if an invalid counter ID was set in the QM_EVTSEL[RMID] field.
>
> Introduce resctrl_arch_reset_cntr() and resctrl_arch_cntr_read() to read
> event data for a specific counter.
hmmm ... they cannot both be used to read the event data?
>
> Signed-off-by: Babu Moger <babu.moger@....com>
> ---
...
> ---
> arch/x86/kernel/cpu/resctrl/internal.h | 6 +++
> arch/x86/kernel/cpu/resctrl/monitor.c | 70 ++++++++++++++++++++++++++
> 2 files changed, 76 insertions(+)
>
> diff --git a/arch/x86/kernel/cpu/resctrl/internal.h b/arch/x86/kernel/cpu/resctrl/internal.h
> index 6bf6042f11b6..ae4003d44df4 100644
> --- a/arch/x86/kernel/cpu/resctrl/internal.h
> +++ b/arch/x86/kernel/cpu/resctrl/internal.h
> @@ -40,6 +40,12 @@ struct arch_mbm_state {
> /* Setting bit 0 in L3_QOS_EXT_CFG enables the ABMC feature. */
> #define ABMC_ENABLE_BIT 0
>
> +/*
> + * Qos Event Identifiers.
> + */
> +#define ABMC_EXTENDED_EVT_ID BIT(31)
> +#define ABMC_EVT_ID BIT(0)
> +
> /**
> * struct rdt_hw_ctrl_domain - Arch private attributes of a set of CPUs that share
> * a resource for a control function
> diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
> index a230d98e9d73..026c2e2d19d3 100644
> --- a/arch/x86/kernel/cpu/resctrl/monitor.c
> +++ b/arch/x86/kernel/cpu/resctrl/monitor.c
> @@ -259,6 +259,76 @@ int resctrl_arch_rmid_read(struct rdt_resource *r, struct rdt_mon_domain *d,
> return 0;
> }
>
> +static int __cntr_id_read(u32 cntr_id, u64 *val)
> +{
> + u64 msr_val;
> +
> + /*
> + * QM_EVTSEL Register definition:
> + * =======================================================
> + * Bits Mnemonic Description
> + * =======================================================
> + * 63:44 -- Reserved
> + * 43:32 RMID Resource Monitoring Identifier
> + * 31 ExtEvtID Extended Event Identifier
> + * 30:8 -- Reserved
> + * 7:0 EvtID Event Identifier
> + * =======================================================
> + * The contents of a specific counter can be read by setting the
> + * following fields in QM_EVTSEL.ExtendedEvtID(=1) and
> + * QM_EVTSEL.EvtID = L3CacheABMC (=1) and setting [RMID] to the
> + * desired counter ID. Reading QM_CTR will then return the
> + * contents of the specified counter. The E bit will be set if the
> + * counter configuration was invalid, or if an invalid counter ID
> + * was set in the QM_EVTSEL[RMID] field.
(same comments as changelog)
> + */
> + wrmsr(MSR_IA32_QM_EVTSEL, ABMC_EXTENDED_EVT_ID | ABMC_EVT_ID, cntr_id);
> + rdmsrl(MSR_IA32_QM_CTR, msr_val);
> +
> + if (msr_val & RMID_VAL_ERROR)
> + return -EIO;
> + if (msr_val & RMID_VAL_UNAVAIL)
> + return -EINVAL;
One of these must be the "E bit" (unclear which), leaving other undefined?
> +
> + *val = msr_val;
> + return 0;
> +}
> +
> +void resctrl_arch_reset_cntr(struct rdt_resource *r, struct rdt_mon_domain *d,
> + u32 unused, u32 rmid, int cntr_id,
> + enum resctrl_event_id eventid)
> +{
> + struct rdt_hw_mon_domain *hw_dom = resctrl_to_arch_mon_dom(d);
> + struct arch_mbm_state *am;
> +
> + am = get_arch_mbm_state(hw_dom, rmid, eventid);
> + if (am) {
> + memset(am, 0, sizeof(*am));
> +
> + /* Record any initial, non-zero count value. */
> + __cntr_id_read(cntr_id, &am->prev_msr);
> + }
> +}
> +
> +int resctrl_arch_cntr_read(struct rdt_resource *r, struct rdt_mon_domain *d,
> + u32 unused, u32 rmid, int cntr_id,
> + enum resctrl_event_id eventid,
> + u64 *val, void *ignored)
> +{
> + u64 msr_val;
> + int ret;
> +
> + resctrl_arch_rmid_read_context_check();
Is this needed? I see this context check as related to the MPAM cache occupancy
counters that need to be allocated when a counter is read (see comments of
resctrl_arch_rmid_read() in include/linux/resctrl.h). To me this does not seem
relevant to this work since all allocations should already have been done
when the counter was allocated, no?
> +
> + ret = __cntr_id_read(cntr_id, &msr_val);
> + if (ret)
> + return ret;
> +
> + *val = mbm_corrected_val(r, d, rmid, eventid, msr_val);
> +
> + return 0;
> +}
> +
> /*
> * The power-on reset value of MSR_RMID_SNC_CONFIG is 0x1
> * which indicates that RMIDs are configured in legacy mode.
Reinette
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