linux-kernel - Re: [PATCH 28/33] arm_mpam: Consider overflow in bandwidth counter state

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Message-ID: <7df04942-5afa-604d-3573-ec54a2c89945@huawei.com>
Date: Mon, 10 Nov 2025 21:50:34 +0800
From: Zeng Heng <zengheng4@...wei.com>
To: Ben Horgan <ben.horgan@....com>, <james.morse@....com>
CC: <amitsinght@...vell.com>, <baisheng.gao@...soc.com>,
	<baolin.wang@...ux.alibaba.com>, <bobo.shaobowang@...wei.com>,
	<carl@...amperecomputing.com>, <catalin.marinas@....com>, <dakr@...nel.org>,
	<dave.martin@....com>, <david@...hat.com>, <dfustini@...libre.com>,
	<fenghuay@...dia.com>, <gregkh@...uxfoundation.org>, <gshan@...hat.com>,
	<guohanjun@...wei.com>, <jeremy.linton@....com>,
	<jonathan.cameron@...wei.com>, <kobak@...dia.com>, <lcherian@...vell.com>,
	<lenb@...nel.org>, <linux-acpi@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>, <linux-kernel@...r.kernel.org>,
	<lpieralisi@...nel.org>, <peternewman@...gle.com>, <quic_jiles@...cinc.com>,
	<rafael@...nel.org>, <robh@...nel.org>, <rohit.mathew@....com>,
	<scott@...amperecomputing.com>, <sdonthineni@...dia.com>,
	<sudeep.holla@....com>, <tan.shaopeng@...itsu.com>, <will@...nel.org>,
	<xhao@...ux.alibaba.com>
Subject: Re: [PATCH 28/33] arm_mpam: Consider overflow in bandwidth counter
 state



On 2025/11/7 20:34, Ben Horgan wrote:
> Use the overflow status bit to track overflow on each bandwidth counter
> read and add the counter size to the correction when overflow is detected.
> 
> This assumes that only a single overflow has occurred since the last read
> of the counter. Overflow interrupts, on hardware that supports them could
> be used to remove this limitation.
> 
> Cc: Zeng Heng <zengheng4@...wei.com>
> Signed-off-by: Ben Horgan <ben.horgan@....com>
> ---
>   drivers/resctrl/mpam_devices.c  | 24 ++++++++++++++++++++++--
>   drivers/resctrl/mpam_internal.h |  3 ++-
>   2 files changed, 24 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/resctrl/mpam_devices.c b/drivers/resctrl/mpam_devices.c
> index 2d1cef824b8e..eea082dfcddc 100644
> --- a/drivers/resctrl/mpam_devices.c
> +++ b/drivers/resctrl/mpam_devices.c
> @@ -986,11 +986,18 @@ static void write_msmon_ctl_flt_vals(struct mon_read *m, u32 ctl_val,
>   	}
>   }
>   
> +static u64 mpam_msmon_overflow_val(enum mpam_device_features type)
> +{
> +	/* TODO: scaling, and long counters */
> +	return BIT_ULL(hweight_long(MSMON___VALUE));
> +}
> +
>   static void __ris_msmon_read(void *arg)
>   {
>   	u64 now;
>   	bool nrdy = false;
>   	bool config_mismatch;
> +	bool overflow;
>   	struct mon_read *m = arg;
>   	struct mon_cfg *ctx = m->ctx;
>   	struct mpam_msc_ris *ris = m->ris;
> @@ -1012,13 +1019,20 @@ static void __ris_msmon_read(void *arg)
>   	 * This saves waiting for 'nrdy' on subsequent reads.
>   	 */
>   	read_msmon_ctl_flt_vals(m, &cur_ctl, &cur_flt);
> +	overflow = cur_ctl & MSMON_CFG_x_CTL_OFLOW_STATUS;
> +
>   	clean_msmon_ctl_val(&cur_ctl);
>   	gen_msmon_ctl_flt_vals(m, &ctl_val, &flt_val);
>   	config_mismatch = cur_flt != flt_val ||
>   			  cur_ctl != (ctl_val | MSMON_CFG_x_CTL_EN);
>   
> -	if (config_mismatch)
> +	if (config_mismatch) {
>   		write_msmon_ctl_flt_vals(m, ctl_val, flt_val);
> +		overflow = false;
> +	} else if (overflow) {
> +		mpam_write_monsel_reg(msc, CFG_MBWU_CTL,
> +				      cur_ctl & ~MSMON_CFG_x_CTL_OFLOW_STATUS);
> +	}
>   
>   	switch (m->type) {
>   	case mpam_feat_msmon_csu:
> @@ -1038,7 +1052,13 @@ static void __ris_msmon_read(void *arg)
>   
>   		mbwu_state = &ris->mbwu_state[ctx->mon];
>   
> -		/* Include bandwidth consumed before the last hardware reset */
> +		if (overflow)
> +			mbwu_state->correction += mpam_msmon_overflow_val(m->type);
> +
> +		/*
> +		 * Include bandwidth consumed before the last hardware reset and
> +		 * a counter size increment for each overflow.
> +		 */
>   		now += mbwu_state->correction;
>   		break;
>   	default:
> diff --git a/drivers/resctrl/mpam_internal.h b/drivers/resctrl/mpam_internal.h
> index 1f2b04b7703e..7c99d4f3dc9c 100644
> --- a/drivers/resctrl/mpam_internal.h
> +++ b/drivers/resctrl/mpam_internal.h
> @@ -209,7 +209,8 @@ struct msmon_mbwu_state {
>   	struct mon_cfg	cfg;
>   
>   	/*
> -	 * The value to add to the new reading to account for power management.
> +	 * The value to add to the new reading to account for power management,
> +	 * and overflow.
>   	 */
>   	u64		correction;
>   

Reviewed-by: Zeng Heng <zengheng4@...wei.com>