RE: [PATCH v6 00/24] x86/resctrl: monitored closid+rmid together, separate arch/fs locking

Shaopeng Tan (Fujitsu)
2023-09-27T07:38:19Z

Hello James,

I reviewed this patch series(v6) and ran resctrl selftest on
Intel(R) Xeon(R) Gold 6254 CPU with nohz_full enabled/disabled,
there is no problem.

<reviewed-by:tan.shaopeng@jp.fujitsu.com>
<tested-by:tan.shaopeng@jp.fujitsu.com>

> This series does two things, it changes resctrl to call resctrl_arch_rmid_read()
> in a way that works for MPAM, and it separates the locking so that the arch
> code and filesystem code don't have to share a mutex. I tried to split this as two
> series, but these touch similar call sites, so it would create more work.
>
> (What's MPAM? See the cover letter of the first series. [1])
>
> On x86 the RMID is an independent number. MPAMs equivalent is PMG, but
> this isn't an independent number - it extends the PARTID (same as CLOSID)
> space with bits that aren't used to select the configuration. The monitors can
> then be told to match specific PMG values, allowing monitor-groups to be
> created.
>
> But, MPAM expects the monitors to always monitor by PARTID. The
> Cache-storage-utilisation counters can only work this way.
> (In the MPAM spec not setting the MATCH_PARTID bit is made
> CONSTRAINED UNPREDICTABLE - which is Arm's term to mean portable
> software can't rely on
> this)
>
> It gets worse, as some SoCs may have very few PMG bits. I've seen the
> datasheet for one that has a single bit of PMG space.
>
> To be usable, MPAM's counters always need the PARTID and the PMG.
> For resctrl, this means always making the CLOSID available when the RMID is
> used.
>
> To ensure RMID are always unique, this series combines the CLOSID and
> RMID into an index, and manages RMID based on that. For x86, the index and
> RMID would always be the same.
>
>
> Currently the architecture specific code in the cpuhp callbacks takes the
> rdtgroup_mutex. This means the filesystem code would have to export this lock,
> resulting in an ill-defined interface between the two, and the possibility of
> cross-architecture lock-ordering head aches.
>
> The second part of this series adds a domain_list_lock to protect writes to the
> domain list, and protects the domain list with RCU - or cpus_read_lock().
>
> Use of RCU is to allow lockless readers of the domain list. To get MPAMs
> monitors working, its very likely they'll need to be plumbed up to perf. An
> uncore PMU driver would need to be a lockless reader of the domain list.
>
> This series is based on v6.6-rc1, and can be retrieved from:
> https://git.kernel.org/pub/scm/linux/kernel/git/morse/linux.git
> mpam/monitors_and_locking/v6
>
> Bugs welcome,
>
> Thanks,
>
> James
>
> [1]
> https://lore.kernel.org/lkml/20210728170637.25610-1-james.morse@arm.com
> /
> [v1]
> https://lore.kernel.org/all/20221021131204.5581-1-james.morse@arm.com/
> [v2]
> https://lore.kernel.org/lkml/20230113175459.14825-1-james.morse@arm.com
> /
> [v3]
> https://lore.kernel.org/r/20230320172620.18254-1-james.morse@arm.com
> [v4]
> https://lore.kernel.org/r/20230525180209.19497-1-james.morse@arm.com
> [v6]
> https://lore.kernel.org/lkml/20230728164254.27562-1-james.morse@arm.com
> /
>
>
> James Morse (24):
> tick/nohz: Move tick_nohz_full_mask declaration outside the #ifdef
> x86/resctrl: kfree() rmid_ptrs from rdtgroup_exit()
> x86/resctrl: Create helper for RMID allocation and mondata dir
> creation
> x86/resctrl: Move rmid allocation out of mkdir_rdt_prepare()
> x86/resctrl: Track the closid with the rmid
> x86/resctrl: Access per-rmid structures by index
> x86/resctrl: Allow RMID allocation to be scoped by CLOSID
> x86/resctrl: Track the number of dirty RMID a CLOSID has
> x86/resctrl: Use set_bit()/clear_bit() instead of open coding
> x86/resctrl: Allocate the cleanest CLOSID by searching
> closid_num_dirty_rmid
> x86/resctrl: Move CLOSID/RMID matching and setting to use helpers
> x86/resctrl: Add cpumask_any_housekeeping() for limbo/overflow
> x86/resctrl: Queue mon_event_read() instead of sending an IPI
> x86/resctrl: Allow resctrl_arch_rmid_read() to sleep
> x86/resctrl: Allow arch to allocate memory needed in
> resctrl_arch_rmid_read()
> x86/resctrl: Make resctrl_mounted checks explicit
> x86/resctrl: Move alloc/mon static keys into helpers
> x86/resctrl: Make rdt_enable_key the arch's decision to switch
> x86/resctrl: Add helpers for system wide mon/alloc capable
> x86/resctrl: Add CPU online callback for resctrl work
> x86/resctrl: Allow overflow/limbo handlers to be scheduled on any-but
> cpu
> x86/resctrl: Add cpu offline callback for resctrl work
> x86/resctrl: Move domain helper migration into resctrl_offline_cpu()
> x86/resctrl: Separate arch and fs resctrl locks
>
> arch/x86/include/asm/resctrl.h | 90 +++++
> arch/x86/kernel/cpu/resctrl/core.c | 78 ++--
> arch/x86/kernel/cpu/resctrl/ctrlmondata.c | 47 ++-
> arch/x86/kernel/cpu/resctrl/internal.h | 56 ++-
> arch/x86/kernel/cpu/resctrl/monitor.c | 434
> +++++++++++++++++-----
> arch/x86/kernel/cpu/resctrl/pseudo_lock.c | 15 +-
> arch/x86/kernel/cpu/resctrl/rdtgroup.c | 345 ++++++++++++-----
> include/linux/resctrl.h | 43 ++-
> include/linux/tick.h | 9 +-
> 9 files changed, 857 insertions(+), 260 deletions(-)
>
> --
> 2.39.2