From: James Morse <james.morse@arm.com>
To: babu.moger@amd.com, x86@kernel.org, linux-kernel@vger.kernel.org
Cc: Fenghua Yu <fenghua.yu@intel.com>,
Reinette Chatre <reinette.chatre@intel.com>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
H Peter Anvin <hpa@zytor.com>,
shameerali.kolothum.thodi@huawei.com,
D Scott Phillips OS <scott@os.amperecomputing.com>,
carl@os.amperecomputing.com, lcherian@marvell.com,
bobo.shaobowang@huawei.com, tan.shaopeng@fujitsu.com,
baolin.wang@linux.alibaba.com,
Jamie Iles <quic_jiles@quicinc.com>,
Xin Hao <xhao@linux.alibaba.com>,
peternewman@google.com, dfustini@baylibre.com,
amitsinght@marvell.com
Subject: Re: [PATCH v8 13/24] x86/resctrl: Queue mon_event_read() instead of sending an IPI
Date: Mon, 22 Jan 2024 18:06:18 +0000 [thread overview]
Message-ID: <93c86af6-7eaa-4cd5-3599-34f2f033a1f5@arm.com> (raw)
In-Reply-To: <cf72ab6a-83b7-4609-8dec-7756f8ae5808@amd.com>
Hi Babu,
On 03/01/2024 19:43, Moger, Babu wrote:
> On 12/15/23 11:43, James Morse wrote:
>> Intel is blessed with an abundance of monitors, one per RMID, that can be
>> read from any CPU in the domain. MPAMs monitors reside in the MMIO MSC,
>> the number implemented is up to the manufacturer. This means when there are
>> fewer monitors than needed, they need to be allocated and freed.
>>
>> MPAM's CSU monitors are used to back the 'llc_occupancy' monitor file. The
>> CSU counter is allowed to return 'not ready' for a small number of
>> micro-seconds after programming. To allow one CSU hardware monitor to be
>> used for multiple control or monitor groups, the CPU accessing the
>> monitor needs to be able to block when configuring and reading the
>> counter.
>>
>> Worse, the domain may be broken up into slices, and the MMIO accesses
>> for each slice may need performing from different CPUs.
>>
>> These two details mean MPAMs monitor code needs to be able to sleep, and
>> IPI another CPU in the domain to read from a resource that has been sliced.
>>
>> mon_event_read() already invokes mon_event_count() via IPI, which means
>> this isn't possible. On systems using nohz-full, some CPUs need to be
>> interrupted to run kernel work as they otherwise stay in user-space
>> running realtime workloads. Interrupting these CPUs should be avoided,
>> and scheduling work on them may never complete.
>>
>> Change mon_event_read() to pick a housekeeping CPU, (one that is not using
>> nohz_full) and schedule mon_event_count() and wait. If all the CPUs
>> in a domain are using nohz-full, then an IPI is used as the fallback.
>>
>> This function is only used in response to a user-space filesystem request
>> (not the timing sensitive overflow code).
>>
>> This allows MPAM to hide the slice behaviour from resctrl, and to keep
>> the monitor-allocation in monitor.c. When the IPI fallback is used on
>> machines where MPAM needs to make an access on multiple CPUs, the counter
>> read will always fail.
> Reviewed-by: Babu Moger <babu.moger@amd.com>
Thanks!
James
next prev parent reply other threads:[~2024-01-22 18:06 UTC|newest]
Thread overview: 50+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-12-15 17:43 [PATCH v8 00/24] x86/resctrl: monitored closid+rmid together, separate arch/fs locking James Morse
2023-12-15 17:43 ` [PATCH v8 01/24] tick/nohz: Move tick_nohz_full_mask declaration outside the #ifdef James Morse
2023-12-15 20:31 ` Thomas Gleixner
2024-01-22 18:05 ` James Morse
2023-12-15 17:43 ` [PATCH v8 02/24] x86/resctrl: kfree() rmid_ptrs from resctrl_exit() James Morse
2023-12-16 4:57 ` Reinette Chatre
2023-12-15 17:43 ` [PATCH v8 03/24] x86/resctrl: Create helper for RMID allocation and mondata dir creation James Morse
2023-12-15 17:43 ` [PATCH v8 04/24] x86/resctrl: Move rmid allocation out of mkdir_rdt_prepare() James Morse
2023-12-15 17:43 ` [PATCH v8 05/24] x86/resctrl: Track the closid with the rmid James Morse
2023-12-16 4:58 ` Reinette Chatre
2024-01-22 18:05 ` James Morse
2023-12-15 17:43 ` [PATCH v8 06/24] x86/resctrl: Access per-rmid structures by index James Morse
2023-12-16 4:58 ` Reinette Chatre
2024-01-22 18:05 ` James Morse
2023-12-15 17:43 ` [PATCH v8 07/24] x86/resctrl: Allow RMID allocation to be scoped by CLOSID James Morse
2023-12-15 17:43 ` [PATCH v8 08/24] x86/resctrl: Track the number of dirty RMID a CLOSID has James Morse
2024-01-03 19:43 ` Moger, Babu
2024-01-22 18:05 ` James Morse
2024-01-04 19:13 ` Peter Newman
2024-01-22 18:05 ` James Morse
2023-12-15 17:43 ` [PATCH v8 09/24] x86/resctrl: Use __set_bit()/__clear_bit() instead of open coding James Morse
2023-12-15 17:43 ` [PATCH v8 10/24] x86/resctrl: Allocate the cleanest CLOSID by searching closid_num_dirty_rmid James Morse
2023-12-16 5:01 ` Reinette Chatre
2024-01-22 18:06 ` James Morse
2023-12-15 17:43 ` [PATCH v8 11/24] x86/resctrl: Move CLOSID/RMID matching and setting to use helpers James Morse
2023-12-15 17:43 ` [PATCH v8 12/24] x86/resctrl: Add cpumask_any_housekeeping() for limbo/overflow James Morse
2023-12-15 17:43 ` [PATCH v8 13/24] x86/resctrl: Queue mon_event_read() instead of sending an IPI James Morse
2024-01-03 19:43 ` Moger, Babu
2024-01-22 18:06 ` James Morse [this message]
2023-12-15 17:43 ` [PATCH v8 14/24] x86/resctrl: Allow resctrl_arch_rmid_read() to sleep James Morse
2024-01-03 19:43 ` Moger, Babu
2024-01-22 18:06 ` James Morse
2023-12-15 17:43 ` [PATCH v8 15/24] x86/resctrl: Allow arch to allocate memory needed in resctrl_arch_rmid_read() James Morse
2023-12-15 17:43 ` [PATCH v8 16/24] x86/resctrl: Make resctrl_mounted checks explicit James Morse
2023-12-15 17:43 ` [PATCH v8 17/24] x86/resctrl: Move alloc/mon static keys into helpers James Morse
2023-12-15 17:43 ` [PATCH v8 18/24] x86/resctrl: Make rdt_enable_key the arch's decision to switch James Morse
2023-12-15 17:43 ` [PATCH v8 19/24] x86/resctrl: Add helpers for system wide mon/alloc capable James Morse
2024-01-03 19:43 ` Moger, Babu
2024-01-22 18:06 ` James Morse
2023-12-15 17:43 ` [PATCH v8 20/24] x86/resctrl: Add CPU online callback for resctrl work James Morse
2023-12-15 17:43 ` [PATCH v8 21/24] x86/resctrl: Allow overflow/limbo handlers to be scheduled on any-but cpu James Morse
2023-12-16 5:02 ` Reinette Chatre
2024-01-22 18:06 ` James Morse
2023-12-15 17:43 ` [PATCH v8 22/24] x86/resctrl: Add CPU offline callback for resctrl work James Morse
2023-12-15 17:43 ` [PATCH v8 23/24] x86/resctrl: Move domain helper migration into resctrl_offline_cpu() James Morse
2023-12-15 17:43 ` [PATCH v8 24/24] x86/resctrl: Separate arch and fs resctrl locks James Morse
2023-12-22 22:43 ` [PATCH v8 00/24] x86/resctrl: monitored closid+rmid together, separate arch/fs locking Carl Worth
2024-01-22 18:06 ` James Morse
2024-01-03 19:42 ` Moger, Babu
2024-01-22 18:06 ` James Morse
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=93c86af6-7eaa-4cd5-3599-34f2f033a1f5@arm.com \
--to=james.morse@arm.com \
--cc=amitsinght@marvell.com \
--cc=babu.moger@amd.com \
--cc=baolin.wang@linux.alibaba.com \
--cc=bobo.shaobowang@huawei.com \
--cc=bp@alien8.de \
--cc=carl@os.amperecomputing.com \
--cc=dfustini@baylibre.com \
--cc=fenghua.yu@intel.com \
--cc=hpa@zytor.com \
--cc=lcherian@marvell.com \
--cc=linux-kernel@vger.kernel.org \
--cc=mingo@redhat.com \
--cc=peternewman@google.com \
--cc=quic_jiles@quicinc.com \
--cc=reinette.chatre@intel.com \
--cc=scott@os.amperecomputing.com \
--cc=shameerali.kolothum.thodi@huawei.com \
--cc=tan.shaopeng@fujitsu.com \
--cc=tglx@linutronix.de \
--cc=x86@kernel.org \
--cc=xhao@linux.alibaba.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).