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Message-ID:
<OSZPR01MB87982A954238E8122FF3ABD58B16A@OSZPR01MB8798.jpnprd01.prod.outlook.com>
Date: Thu, 18 Sep 2025 02:35:30 +0000
From: "Shaopeng Tan (Fujitsu)" <tan.shaopeng@...itsu.com>
To: 'James Morse' <james.morse@....com>, "linux-kernel@...r.kernel.org"
<linux-kernel@...r.kernel.org>, "linux-arm-kernel@...ts.infradead.org"
<linux-arm-kernel@...ts.infradead.org>, "linux-acpi@...r.kernel.org"
<linux-acpi@...r.kernel.org>
CC: D Scott Phillips OS <scott@...amperecomputing.com>,
"carl@...amperecomputing.com" <carl@...amperecomputing.com>,
"lcherian@...vell.com" <lcherian@...vell.com>, "bobo.shaobowang@...wei.com"
<bobo.shaobowang@...wei.com>, "baolin.wang@...ux.alibaba.com"
<baolin.wang@...ux.alibaba.com>, Jamie Iles <quic_jiles@...cinc.com>, Xin Hao
<xhao@...ux.alibaba.com>, "peternewman@...gle.com" <peternewman@...gle.com>,
"dfustini@...libre.com" <dfustini@...libre.com>, "amitsinght@...vell.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" <fenghuay@...dia.com>,
"baisheng.gao@...soc.com" <baisheng.gao@...soc.com>, Jonathan Cameron
<jonathan.cameron@...wei.com>, Rob Herring <robh@...nel.org>, Rohit Mathew
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<lenb@...nel.org>, Lorenzo Pieralisi <lpieralisi@...nel.org>, Hanjun Guo
<guohanjun@...wei.com>, Sudeep Holla <sudeep.holla@....com>, 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 27/29] arm_mpam: Add helper to reset saved mbwu state
Hello James
> resctrl expects to reset the bandwidth counters when the filesystem is
> mounted.
>
> To allow this, add a helper that clears the saved mbwu state. Instead of cross
> calling to each CPU that can access the component MSC to write to the counter,
> set a flag that causes it to be zero'd on the the next read. This is easily done by
> forcing a configuration update.
>
> Signed-off-by: James Morse <james.morse@....com>
> ---
> drivers/resctrl/mpam_devices.c | 47
> +++++++++++++++++++++++++++++++--
> drivers/resctrl/mpam_internal.h | 5 +++-
> 2 files changed, 49 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/resctrl/mpam_devices.c b/drivers/resctrl/mpam_devices.c
> index 3080a81f0845..8254d6190ca2 100644
> --- a/drivers/resctrl/mpam_devices.c
> +++ b/drivers/resctrl/mpam_devices.c
> @@ -1088,9 +1088,11 @@ static u64 mpam_msmon_overflow_val(struct
> mpam_msc_ris *ris) static void __ris_msmon_read(void *arg) {
> bool nrdy = false;
> + bool config_mismatch;
> struct mon_read *m = arg;
> u64 now, overflow_val = 0;
> struct mon_cfg *ctx = m->ctx;
> + bool reset_on_next_read = false;
> struct mpam_msc_ris *ris = m->ris;
> struct msmon_mbwu_state *mbwu_state;
> struct mpam_props *rprops = &ris->props; @@ -1105,6 +1107,14 @@
> static void __ris_msmon_read(void *arg)
> FIELD_PREP(MSMON_CFG_MON_SEL_RIS, ris->ris_idx);
> mpam_write_monsel_reg(msc, CFG_MON_SEL, mon_sel);
>
> + if (m->type == mpam_feat_msmon_mbwu) {
> + mbwu_state = &ris->mbwu_state[ctx->mon];
> + if (mbwu_state) {
> + reset_on_next_read =
> mbwu_state->reset_on_next_read;
> + mbwu_state->reset_on_next_read = false;
> + }
> + }
> +
> /*
> * Read the existing configuration to avoid re-writing the same values.
> * This saves waiting for 'nrdy' on subsequent reads.
> @@ -1112,7 +1122,10 @@ static void __ris_msmon_read(void *arg)
> read_msmon_ctl_flt_vals(m, &cur_ctl, &cur_flt);
> clean_msmon_ctl_val(&cur_ctl);
> gen_msmon_ctl_flt_vals(m, &ctl_val, &flt_val);
> - if (cur_flt != flt_val || cur_ctl != (ctl_val | MSMON_CFG_x_CTL_EN))
> + config_mismatch = cur_flt != flt_val ||
> + cur_ctl != (ctl_val | MSMON_CFG_x_CTL_EN);
> +
> + if (config_mismatch || reset_on_next_read)
> write_msmon_ctl_flt_vals(m, ctl_val, flt_val);
mbm_handle_overflow() calls __ris_msmon_read() every second.
If there are multiple monitor groups, the config_mismatch will "true" every second.
Then "mbwu_state->prev_val = 0;" in function write_msmon_ctl_flt_vals() will be always run.
This means that for multiple monitoring groups, the MemoryBandwidth monitoring value is cleared every second.
https://lore.kernel.org/lkml/20250910204309.20751-25-james.morse@arm.com/
+ mbwu_state = &m->ris->mbwu_state[m->ctx->mon];
+ if (mbwu_state)
+ mbwu_state->prev_val = 0;
Best regards,
Shaopeng TAN
> switch (m->type) {
> @@ -1145,7 +1158,6 @@ static void __ris_msmon_read(void *arg)
> if (nrdy)
> break;
>
> - mbwu_state = &ris->mbwu_state[ctx->mon];
> if (!mbwu_state)
> break;
>
> @@ -1245,6 +1257,37 @@ int mpam_msmon_read(struct mpam_component
> *comp, struct mon_cfg *ctx,
> return err;
> }
>
> +void mpam_msmon_reset_mbwu(struct mpam_component *comp, struct
> mon_cfg
> +*ctx) {
> + int idx;
> + struct mpam_msc *msc;
> + struct mpam_vmsc *vmsc;
> + struct mpam_msc_ris *ris;
> +
> + if (!mpam_is_enabled())
> + return;
> +
> + idx = srcu_read_lock(&mpam_srcu);
> + list_for_each_entry_rcu(vmsc, &comp->vmsc, comp_list) {
> + if (!mpam_has_feature(mpam_feat_msmon_mbwu,
> &vmsc->props))
> + continue;
> +
> + msc = vmsc->msc;
> + list_for_each_entry_rcu(ris, &vmsc->ris, vmsc_list) {
> + if (!mpam_has_feature(mpam_feat_msmon_mbwu,
> &ris->props))
> + continue;
> +
> + if (WARN_ON_ONCE(!mpam_mon_sel_lock(msc)))
> + continue;
> +
> + ris->mbwu_state[ctx->mon].correction = 0;
> + ris->mbwu_state[ctx->mon].reset_on_next_read =
> true;
> + mpam_mon_sel_unlock(msc);
> + }
> + }
> + srcu_read_unlock(&mpam_srcu, idx);
> +}
> +
> static void mpam_reset_msc_bitmap(struct mpam_msc *msc, u16 reg, u16
> wd) {
> u32 num_words, msb;
> diff --git a/drivers/resctrl/mpam_internal.h
> b/drivers/resctrl/mpam_internal.h index c190826dfbda..7cbcafe8294a 100644
> --- a/drivers/resctrl/mpam_internal.h
> +++ b/drivers/resctrl/mpam_internal.h
> @@ -223,10 +223,12 @@ struct mon_cfg {
>
> /*
> * Changes to enabled and cfg are protected by the msc->lock.
> - * Changes to prev_val and correction are protected by the msc's
> mon_sel_lock.
> + * Changes to reset_on_next_read, prev_val and correction are protected
> + by the
> + * msc's mon_sel_lock.
> */
> struct msmon_mbwu_state {
> bool enabled;
> + bool reset_on_next_read;
> struct mon_cfg cfg;
>
> /* The value last read from the hardware. Used to detect overflow. */
> @@ -393,6 +395,7 @@ int mpam_apply_config(struct mpam_component
> *comp, u16 partid,
>
> int mpam_msmon_read(struct mpam_component *comp, struct mon_cfg
> *ctx,
> enum mpam_device_features, u64 *val);
> +void mpam_msmon_reset_mbwu(struct mpam_component *comp, struct
> mon_cfg
> +*ctx);
>
> int mpam_get_cpumask_from_cache_id(unsigned long cache_id, u32
> cache_level,
> cpumask_t *affinity);
> --
> 2.39.5
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