Date: Tue, 13 Feb 2024 15:26:56 -0800
From: Reinette Chatre <reinette.chatre@...el.com>
To: James Morse <james.morse@....com>, <x86@...nel.org>,
	<linux-kernel@...r.kernel.org>, Borislav Petkov <bp@...en8.de>
CC: Fenghua Yu <fenghua.yu@...el.com>, Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, H Peter Anvin <hpa@...or.com>, Babu Moger
	<Babu.Moger@....com>, <shameerali.kolothum.thodi@...wei.com>, "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>, "Luck, Tony" <tony.luck@...el.com>
Subject: Re: [PATCH v9 00/24] x86/resctrl: monitored closid+rmid together,
 separate arch/fs locking

(+Tony)

Hi Boris,

Could you please consider this series for inclusion?

Thank you very much.

Reinette

On 2/13/2024 10:44 AM, James Morse wrote:
> Hello!
> 
> It's been back and forth for whether this series should be rebased onto Tony's
> SNC series. This version isn't, its based on tip/x86/cache.
> (I have the rebased-and-tested versions if anyone needs them)
> 
> This version just has minor cleanup from the previous one.
> * An unusued parameter in unused code has gone,
> * I've added a comment about the sizeing of the index array - it only matters on arm64.
> 
> Changes are also noted on each patch.
> 
> ~
> 
> 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 tip/x86/caches's commit fc747eebef73, and can be retrieved from:
> https://git.kernel.org/pub/scm/linux/kernel/git/morse/linux.git mpam/monitors_and_locking/v9
> 
> 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
> [v5] https://lore.kernel.org/lkml/20230728164254.27562-1-james.morse@arm.com/
> [v6] https://lore.kernel.org/all/20230914172138.11977-1-james.morse@arm.com/
> [v7] https://lore.kernel.org/r/20231025180345.28061-1-james.morse@arm.com/
> [v8] https://lore.kernel.org/lkml/20231215174343.13872-1-james.morse@arm.com/
> 
> James Morse (24):
>   tick/nohz: Move tick_nohz_full_mask declaration outside the #ifdef
>   x86/resctrl: kfree() rmid_ptrs from resctrl_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        | 102 ++---
>  arch/x86/kernel/cpu/resctrl/ctrlmondata.c |  48 ++-
>  arch/x86/kernel/cpu/resctrl/internal.h    |  67 +++-
>  arch/x86/kernel/cpu/resctrl/monitor.c     | 463 +++++++++++++++++-----
>  arch/x86/kernel/cpu/resctrl/pseudo_lock.c |  15 +-
>  arch/x86/kernel/cpu/resctrl/rdtgroup.c    | 359 ++++++++++++-----
>  include/linux/resctrl.h                   |  48 ++-
>  include/linux/tick.h                      |   9 +-
>  9 files changed, 921 insertions(+), 280 deletions(-)
> 

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