linux-kernel - Re: [PATCH v2 24/29] arm_mpam: Track bandwidth counter state for overflow and power management

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Message-ID: <d009edc0-651e-4815-89de-19c419ba0183@arm.com>
Date: Thu, 9 Oct 2025 18:48:56 +0100
From: James Morse <james.morse@....com>
To: Jonathan Cameron <jonathan.cameron@...wei.com>
Cc: linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
 linux-acpi@...r.kernel.org,
 D Scott Phillips OS <scott@...amperecomputing.com>,
 carl@...amperecomputing.com, lcherian@...vell.com,
 bobo.shaobowang@...wei.com, tan.shaopeng@...itsu.com,
 baolin.wang@...ux.alibaba.com, Jamie Iles <quic_jiles@...cinc.com>,
 Xin Hao <xhao@...ux.alibaba.com>, peternewman@...gle.com,
 dfustini@...libre.com, amitsinght@...vell.com,
 David Hildenbrand <david@...hat.com>, Dave Martin <dave.martin@....com>,
 Koba Ko <kobak@...dia.com>, Shanker Donthineni <sdonthineni@...dia.com>,
 fenghuay@...dia.com, baisheng.gao@...soc.com, Rob Herring <robh@...nel.org>,
 Rohit Mathew <rohit.mathew@....com>, Rafael Wysocki <rafael@...nel.org>,
 Len Brown <lenb@...nel.org>, Lorenzo Pieralisi <lpieralisi@...nel.org>,
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 Catalin Marinas <catalin.marinas@....com>, Will Deacon <will@...nel.org>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 Danilo Krummrich <dakr@...nel.org>
Subject: Re: [PATCH v2 24/29] arm_mpam: Track bandwidth counter state for
 overflow and power management

Hi Jonathan,

On 12/09/2025 14:24, Jonathan Cameron wrote:
> On Wed, 10 Sep 2025 20:43:04 +0000
> James Morse <james.morse@....com> wrote:
> 
>> Bandwidth counters need to run continuously to correctly reflect the
>> bandwidth.
>>
>> The value read may be lower than the previous value read in the case
>> of overflow and when the hardware is reset due to CPU hotplug.
>>
>> Add struct mbwu_state to track the bandwidth counter to allow overflow
>> and power management to be handled.
>>
>> Signed-off-by: James Morse <james.morse@....com>

> Trivial comment inline.  I haven't spent enough time thinking about this
> to give a proper review so no tags yet.

>> diff --git a/drivers/resctrl/mpam_devices.c b/drivers/resctrl/mpam_devices.c
>> index 1543c33c5d6a..eeb62ed94520 100644
>> --- a/drivers/resctrl/mpam_devices.c
>> +++ b/drivers/resctrl/mpam_devices.c
>> @@ -918,6 +918,7 @@ static void gen_msmon_ctl_flt_vals(struct mon_read *m, u32 *ctl_val,
>>  	*ctl_val |= MSMON_CFG_x_CTL_MATCH_PARTID;
>>  
>>  	*flt_val = FIELD_PREP(MSMON_CFG_x_FLT_PARTID, ctx->partid);
>> +

> Unrelated change.  If it makes sense figure out where to push it back to.

Done. This is may favourite mistake to make with a merge conflict!


Thanks,

James


>>  	if (m->ctx->match_pmg) {
>>  		*ctl_val |= MSMON_CFG_x_CTL_MATCH_PMG;
>>  		*flt_val |= FIELD_PREP(MSMON_CFG_x_FLT_PMG, ctx->pmg);
>