resctrl_arch_rmid_read(9)

💅 resctrl_arch_rmid_read(9) — Kernel API Manual 🎀

okay so bestie, welcome to the glow-up page for resctrl_arch_rmid_read — it's a kernel API function and honestly it's giving "quietly important" main character energy. Let's get into it ✨

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🌸 NAME 🌸

resctrl_arch_rmid_read — read the eventid counter corresponding to rmid for this resource and domain. That's it, that's the whole vibe 🫶

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⭐ SYNOPSIS ⭐

int resctrl_arch_rmid_read (struct rdt_resource *r , struct
rdt_domain_hdr *hdr , u32 closid , u32 rmid , enum resctrl_event_id
eventid , void *arch_priv , u64 *val , void *arch_mon_ctx );

Like, look at all those parameters. She's thriving 💜

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🦋 ARGUMENTS 🦋

• r — the resource you're pulling the counter from. Your source of truth, your origin story 💫
• hdr — header of the domain that the counter should be read from. Gotta know where you're reading, bestie.
• closid — the closid that matches the rmid. Depending on the architecture, the counter may match traffic of both closid and rmid, or rmid only. So like… architecture-dependent, no cap 🤷‍♀️
• rmid — the rmid of the counter you wanna read. This is the one, the icon, the legend 👑
• eventid — the eventid to read, e.g. L3 occupancy. Pick your fighter 🥊
• arch_priv — architecture private data for this event. This is the arch_priv that the architecture provided via resctrl_enable_mon_event. Very "iykyk" energy 💅
• val — the result of the counter read, in bytes. Slay, units matter 📏
• arch_mon_ctx — an architecture specific value from resctrl_arch_mon_ctx_alloc. For MPAM, this identifies the hardware monitor allocated for this read request. It's the lil hall pass for the hardware monitor 🎟️

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💖 DESCRIPTION 💖

okay so here's the tea ☕ — some architectures need to sleep when first programming some of the counters. and like, specifically? arm64's MPAM cache occupancy counters can return 'not ready' for a short period of time 😭 so rude of them, honestly.

So the rule is: call this from a non-migrateable process context on a CPU that belongs to domain d. e.g. use smp_call_on_cpu or schedule_work_on. That's the correct, well-behaved way to do it 🧚

This function can be called with interrupts masked, e.g. using smp_call_function_any, but it may consistently return an error. So like… technically allowed, but lowkey a trap 🙈

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🔥 RETURN 🔥

0 on success, or -EIO, -EINVAL etc on error. That's the whole return section, she's short and she knows it 💀

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🌈 SEE ALSO 🌈

Kernel file ./include/linux/resctrl.h plus the whole friend group:

• enum resctrl_conf_type(9)
• struct resctrl_staged_config(9)
• struct rdt_domain_hdr(9)
• struct rdt_ctrl_domain(9)
• struct mbm_cntr_cfg(9)
• struct rdt_l3_mon_domain(9)
• struct resctrl_cache(9)
• enum membw_throttle_mode(9)
• struct resctrl_membw(9)
• enum resctrl_schema_fmt(9)
• struct resctrl_mon(9)
• struct rdt_resource(9)
• struct resctrl_schema(9)
• resctrl_arch_sync_cpu_closid_rmid(9)
• resctrl_get_default_ctrl(9)
• resctrl_arch_mon_event_config_write(9)
• resctrl_arch_mon_event_config_read(9)
• resctrl_arch_mbm_cntr_assign_enabled(9)
• resctrl_arch_mbm_cntr_assign_set(9)
• resctrl_arch_rmid_read_context_check(9)
• resctrl_find_domain(9)
• resctrl_arch_reset_rmid(9)
• resctrl_arch_reset_rmid_all(9)
• resctrl_arch_reset_all_ctrls(9)
• resctrl_arch_config_cntr(9)
• resctrl_arch_cntr_read(9)
• resctrl_arch_reset_cntr(9)
• resctrl_arch_io_alloc_enable(9)
• resctrl_arch_get_io_alloc_enabled(9)

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🍓 sign-off 🍓

this little masterpiece lives under ./include/linux, and she was October 2026-coded 🗓️✨ periodt, go read your counters responsibly bestie 💜🦋🌸