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Date: Thu, 9 Nov 2023 09:48:31 -0800
From: Reinette Chatre <reinette.chatre@...el.com>
To: James Morse <james.morse@....com>, <x86@...nel.org>,
<linux-kernel@...r.kernel.org>
CC: Fenghua Yu <fenghua.yu@...el.com>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
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>
Subject: Re: [PATCH v7 21/24] x86/resctrl: Allow overflow/limbo handlers to be
scheduled on any-but cpu
Hi James,
On 10/25/2023 11:03 AM, James Morse wrote:
> When a CPU is taken offline resctrl may need to move the overflow or
> limbo handlers to run on a different CPU.
>
> Once the offline callbacks have been split, cqm_setup_limbo_handler()
> will be called while the CPU that is going offline is still present
> in the cpu_mask.
>
> Pass the CPU to exclude to cqm_setup_limbo_handler() and
> mbm_setup_overflow_handler(). These functions can use a variant of
> cpumask_any_but() when selecting the CPU. -1 is used to indicate no CPUs
> need excluding.
>
> A subsequent patch moves these calls to be before CPUs have been removed,
> so this exclude_cpus behaviour is temporary.
Note "A subsequent patch". Please do go over your entire series. I may not
have noticed all.
>
> Tested-by: Shaopeng Tan <tan.shaopeng@...itsu.com>
> Tested-by: Peter Newman <peternewman@...gle.com>
> Reviewed-by: Shaopeng Tan <tan.shaopeng@...itsu.com>
> Signed-off-by: James Morse <james.morse@....com>
> ---
> Changes since v2:
> * Rephrased a comment to avoid a two letter bad-word. (we)
> * Avoid assigning mbm_work_cpu if the domain is going to be free()d
> * Added cpumask_any_housekeeping_but(), I dislike the name
>
> Changes since v3:
> * Marked an explanatory comment as temporary as the subsequent patch is
> no longer adjacent.
>
> Changes since v4:
> * Check against RESCTRL_PICK_ANY_CPU instead of -1.
> * Leave cqm_work_cpu as nr_cpu_ids when no CPU is available.
> * Made cpumask_any_housekeeping_but() more readable.
>
> Changes since v5:
> * Changes in captialisation, and a typo.
> * Merged cpumask helpers.
>
> Changes since v6:
> * Added the missing dom parameter to some kernel doc.
> * Re-added use of cpumask_any_but(),
> * Expanded comment above cpumask_any_housekeeping(),
> * Added some more comments for good measure.
> * Added explicit IS_ENABLED() check as gcc-12 doesn't seem to work this out.
> ---
> arch/x86/kernel/cpu/resctrl/core.c | 8 +++--
> arch/x86/kernel/cpu/resctrl/ctrlmondata.c | 2 +-
> arch/x86/kernel/cpu/resctrl/internal.h | 33 ++++++++++++++----
> arch/x86/kernel/cpu/resctrl/monitor.c | 42 ++++++++++++++++++-----
> arch/x86/kernel/cpu/resctrl/rdtgroup.c | 6 ++--
> include/linux/resctrl.h | 2 ++
> 6 files changed, 72 insertions(+), 21 deletions(-)
>
> diff --git a/arch/x86/kernel/cpu/resctrl/core.c b/arch/x86/kernel/cpu/resctrl/core.c
> index 1a74e9c47416..7e44f2c40897 100644
> --- a/arch/x86/kernel/cpu/resctrl/core.c
> +++ b/arch/x86/kernel/cpu/resctrl/core.c
> @@ -586,12 +586,16 @@ static void domain_remove_cpu(int cpu, struct rdt_resource *r)
> if (r == &rdt_resources_all[RDT_RESOURCE_L3].r_resctrl) {
> if (is_mbm_enabled() && cpu == d->mbm_work_cpu) {
> cancel_delayed_work(&d->mbm_over);
> - mbm_setup_overflow_handler(d, 0);
> + /*
> + * temporary: exclude_cpu=-1 as this CPU has already
> + * been removed by cpumask_clear_cpu()d
> + */
> + mbm_setup_overflow_handler(d, 0, RESCTRL_PICK_ANY_CPU);
> }
> if (is_llc_occupancy_enabled() && cpu == d->cqm_work_cpu &&
> has_busy_rmid(d)) {
> cancel_delayed_work(&d->cqm_limbo);
> - cqm_setup_limbo_handler(d, 0);
> + cqm_setup_limbo_handler(d, 0, RESCTRL_PICK_ANY_CPU);
> }
> }
> }
> diff --git a/arch/x86/kernel/cpu/resctrl/ctrlmondata.c b/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
> index a033e8e32108..64db51455df3 100644
> --- a/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
> +++ b/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
> @@ -552,7 +552,7 @@ void mon_event_read(struct rmid_read *rr, struct rdt_resource *r,
> return;
> }
>
> - cpu = cpumask_any_housekeeping(&d->cpu_mask);
> + cpu = cpumask_any_housekeeping(&d->cpu_mask, RESCTRL_PICK_ANY_CPU);
>
> /*
> * cpumask_any_housekeeping() prefers housekeeping CPUs, but
> diff --git a/arch/x86/kernel/cpu/resctrl/internal.h b/arch/x86/kernel/cpu/resctrl/internal.h
> index c4c1e1909058..f5fff2f0d866 100644
> --- a/arch/x86/kernel/cpu/resctrl/internal.h
> +++ b/arch/x86/kernel/cpu/resctrl/internal.h
> @@ -61,19 +61,36 @@
> * cpumask_any_housekeeping() - Choose any CPU in @mask, preferring those that
> * aren't marked nohz_full
> * @mask: The mask to pick a CPU from.
> + * @exclude_cpu:The CPU to avoid picking.
> *
> - * Returns a CPU in @mask. If there are housekeeping CPUs that don't use
> - * nohz_full, these are preferred.
> + * Returns a CPU from @mask, but not @exclude_cpu. If there are housekeeping
> + * CPUs that don't use nohz_full, these are preferred. Pass
> + * RESCTRL_PICK_ANY_CPU to avoid excluding any CPUs.
> + *
> + * When a CPU is excluded, returns >= nr_cpu_ids if no CPUs are available.
> */
> -static inline unsigned int cpumask_any_housekeeping(const struct cpumask *mask)
> +static inline unsigned int
> +cpumask_any_housekeeping(const struct cpumask *mask, int exclude_cpu)
> {
> unsigned int cpu, hk_cpu;
>
> - cpu = cpumask_any(mask);
> - if (!tick_nohz_full_cpu(cpu))
> + if (exclude_cpu == RESCTRL_PICK_ANY_CPU)
> + cpu = cpumask_any(mask);
> + else
> + cpu = cpumask_any_but(mask, exclude_cpu);
> +
> + if (!IS_ENABLED(CONFIG_NO_HZ_FULL))
> + return cpu;
It is not clear to me how cpumask_any_but() failure is handled.
cpumask_any_but() returns ">= nr_cpu_ids if no cpus set" ...
> +
> + /* If the CPU picked isn't marked nohz_full, we're done */
Please don't impersonate code.
> + if (cpu <= nr_cpu_ids && !tick_nohz_full_cpu(cpu))
> return cpu;
Is this intended to be "cpu < nr_cpu_ids"? But that would have
code continue ... so maybe it needs explicit error check of
cpumask_any_but() failure with an earlier exit?
>
> + /* Try to find a CPU that isn't nohz_full to use in preference */
> hk_cpu = cpumask_nth_andnot(0, mask, tick_nohz_full_mask);
> + if (hk_cpu == exclude_cpu)
> + hk_cpu = cpumask_nth_andnot(1, mask, tick_nohz_full_mask);
> +
> if (hk_cpu < nr_cpu_ids)
> cpu = hk_cpu;
>
Reinette
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