From: Reinette Chatre <reinette.chatre@intel.com>
To: James Morse <james.morse@arm.com>, <x86@kernel.org>,
<linux-kernel@vger.kernel.org>
Cc: Fenghua Yu <fenghua.yu@intel.com>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
H Peter Anvin <hpa@zytor.com>, Babu Moger <Babu.Moger@amd.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>,
<xingxin.hx@openanolis.org>, <baolin.wang@linux.alibaba.com>,
Jamie Iles <quic_jiles@quicinc.com>,
Xin Hao <xhao@linux.alibaba.com>, <peternewman@google.com>
Subject: Re: [PATCH v3 09/19] x86/resctrl: Queue mon_event_read() instead of sending an IPI
Date: Fri, 31 Mar 2023 16:25:40 -0700 [thread overview]
Message-ID: <5e6a2e0a-6f31-c9b0-5eec-346fd072d286@intel.com> (raw)
In-Reply-To: <20230320172620.18254-10-james.morse@arm.com>
Hi James,
On 3/20/2023 10:26 AM, James Morse wrote:
> x86 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.
>
> 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.
It is not clear to me where in this solution an IPI is used as fallback ...
(see below)
> + int cpu;
> +
> + /* When picking a CPU from cpu_mask, ensure it can't race with cpuhp */
> + lockdep_assert_held(&rdtgroup_mutex);
> +
> /*
> - * setup the parameters to send to the IPI to read the data.
> + * setup the parameters to pass to mon_event_count() to read the data.
> */
> rr->rgrp = rdtgrp;
> rr->evtid = evtid;
> @@ -537,7 +543,16 @@ void mon_event_read(struct rmid_read *rr, struct rdt_resource *r,
> rr->val = 0;
> rr->first = first;
>
> - smp_call_function_any(&d->cpu_mask, mon_event_count, rr, 1);
> + cpu = get_cpu();
> + if (cpumask_test_cpu(cpu, &d->cpu_mask)) {
> + mon_event_count(rr);
> + put_cpu();
> + } else {
> + put_cpu();
> +
> + cpu = cpumask_any_housekeeping(&d->cpu_mask);
> + smp_call_on_cpu(cpu, mon_event_count, rr, false);
> + }
> }
>
... from what I can tell there is no IPI fallback here. As per previous
patch I understand cpumask_any_housekeeping() could still return
a nohz_full CPU and calling smp_call_on_cpu() on it would not send
an IPI but instead queue the work to it. What did I miss?
Reinette
next prev parent reply other threads:[~2023-03-31 23:25 UTC|newest]
Thread overview: 70+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-03-20 17:26 [PATCH v3 00/19] x86/resctrl: monitored closid+rmid together, separate arch/fs locking James Morse
2023-03-20 17:26 ` [PATCH v3 01/19] x86/resctrl: Track the closid with the rmid James Morse
2023-03-20 17:26 ` [PATCH v3 02/19] x86/resctrl: Access per-rmid structures by index James Morse
2023-03-21 10:57 ` Ilpo Järvinen
2023-03-31 23:19 ` Reinette Chatre
2023-04-24 13:06 ` Peter Newman
2023-05-25 17:32 ` James Morse
2023-03-20 17:26 ` [PATCH v3 03/19] x86/resctrl: Create helper for RMID allocation and mondata dir creation James Morse
2023-03-21 11:05 ` Ilpo Järvinen
2023-03-31 23:20 ` Reinette Chatre
2023-03-20 17:26 ` [PATCH v3 04/19] x86/resctrl: Move rmid allocation out of mkdir_rdt_prepare() James Morse
2023-03-20 17:26 ` [PATCH v3 05/19] x86/resctrl: Allow RMID allocation to be scoped by CLOSID James Morse
2023-03-21 11:29 ` Ilpo Järvinen
2023-03-20 17:26 ` [PATCH v3 06/19] x86/resctrl: Allow the allocator to check if a CLOSID can allocate clean RMID James Morse
2023-03-31 23:21 ` Reinette Chatre
2023-04-27 14:09 ` James Morse
2023-03-20 17:26 ` [PATCH v3 07/19] x86/resctrl: Move CLOSID/RMID matching and setting to use helpers James Morse
2023-03-20 17:26 ` [PATCH v3 08/19] x86/resctrl: Add cpumask_any_housekeeping() for limbo/overflow James Morse
2023-03-21 13:21 ` Ilpo Järvinen
2023-04-27 14:09 ` James Morse
2023-03-21 15:14 ` Ilpo Järvinen
2023-04-27 14:09 ` James Morse
2023-04-27 14:25 ` Ilpo Järvinen
2023-05-25 17:32 ` James Morse
2023-03-31 23:24 ` Reinette Chatre
2023-04-27 14:10 ` James Morse
2023-04-27 23:36 ` Reinette Chatre
2023-05-25 17:32 ` James Morse
2023-03-20 17:26 ` [PATCH v3 09/19] x86/resctrl: Queue mon_event_read() instead of sending an IPI James Morse
2023-03-22 14:07 ` Peter Newman
2023-03-23 9:09 ` Peter Newman
2023-04-27 14:12 ` James Morse
2023-04-27 14:11 ` James Morse
2023-03-31 23:25 ` Reinette Chatre [this message]
2023-04-27 14:12 ` James Morse
2023-03-20 17:26 ` [PATCH v3 10/19] x86/resctrl: Allow resctrl_arch_rmid_read() to sleep James Morse
2023-03-31 23:26 ` Reinette Chatre
2023-04-27 14:12 ` James Morse
2023-03-20 17:26 ` [PATCH v3 11/19] x86/resctrl: Allow arch to allocate memory needed in resctrl_arch_rmid_read() James Morse
2023-03-31 23:27 ` Reinette Chatre
2023-04-27 14:19 ` James Morse
2023-04-27 23:40 ` Reinette Chatre
2023-05-25 17:31 ` James Morse
2023-03-20 17:26 ` [PATCH v3 12/19] x86/resctrl: Make resctrl_mounted checks explicit James Morse
2023-03-31 23:28 ` Reinette Chatre
2023-04-27 14:19 ` James Morse
2023-04-27 23:37 ` Reinette Chatre
2023-05-25 17:31 ` James Morse
2023-03-20 17:26 ` [PATCH v3 13/19] x86/resctrl: Move alloc/mon static keys into helpers James Morse
2023-03-20 17:26 ` [PATCH v3 14/19] x86/resctrl: Make rdt_enable_key the arch's decision to switch James Morse
2023-03-20 17:26 ` [PATCH v3 15/19] x86/resctrl: Add helpers for system wide mon/alloc capable James Morse
2023-03-31 23:29 ` Reinette Chatre
2023-04-27 14:19 ` James Morse
2023-03-20 17:26 ` [PATCH v3 16/19] x86/resctrl: Add cpu online callback for resctrl work James Morse
2023-03-31 23:29 ` Reinette Chatre
2023-03-20 17:26 ` [PATCH v3 17/19] x86/resctrl: Allow overflow/limbo handlers to be scheduled on any-but cpu James Morse
2023-03-21 15:12 ` Ilpo Järvinen
2023-03-21 15:25 ` Ilpo Järvinen
2023-04-27 14:20 ` James Morse
2023-03-20 17:26 ` [PATCH v3 18/19] x86/resctrl: Add cpu offline callback for resctrl work James Morse
2023-03-21 15:32 ` Ilpo Järvinen
2023-04-27 14:20 ` James Morse
2023-04-27 14:51 ` Ilpo Järvinen
2023-04-05 23:48 ` Reinette Chatre
2023-04-27 14:20 ` James Morse
2023-03-20 17:26 ` [PATCH v3 19/19] x86/resctrl: Separate arch and fs resctrl locks James Morse
2023-05-23 17:14 ` [PATCH v3 00/19] x86/resctrl: monitored closid+rmid together, separate arch/fs locking Tony Luck
2023-05-25 17:31 ` James Morse
2023-05-25 21:00 ` Tony Luck
2023-05-28 20:52 ` Drew Fustini
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