From: James Morse <james.morse@arm.com>
To: Reinette Chatre <reinette.chatre@intel.com>, fenghua.yu@intel.com
Cc: tglx@linutronix.de, bp@alien8.de, tony.luck@intel.com,
kuo-lang.tseng@intel.com, shakeelb@google.com,
valentin.schneider@arm.com, mingo@redhat.com, babu.moger@amd.com,
hpa@zytor.com, x86@kernel.org, linux-kernel@vger.kernel.org,
stable@vger.kernel.org
Subject: Re: [PATCH 1/3] x86/resctrl: Move setting task's active CPU in a mask into helpers
Date: Wed, 9 Dec 2020 16:47:43 +0000 [thread overview]
Message-ID: <a782d2f3-d2f6-795f-f4b1-9462205fd581@arm.com> (raw)
In-Reply-To: <77973e75a10bf7ef9b33c664544667deee9e1a8e.1607036601.git.reinette.chatre@intel.com>
Hi Reinette, Fenghua,
On 03/12/2020 23:25, Reinette Chatre wrote:
> From: Fenghua Yu <fenghua.yu@intel.com>
>
> The code of setting the CPU on which a task is running in a CPU mask is
> moved into a couple of helpers. The new helper task_on_cpu() will be
> reused shortly.
> diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> index 6f4ca4bea625..68db7d2dec8f 100644
> --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> @@ -525,6 +525,38 @@ static void rdtgroup_remove(struct rdtgroup *rdtgrp)
> +#ifdef CONFIG_SMP
(using IS_ENABLED(CONFIG_SMP) lets the compiler check all the code in one go, then
dead-code-remove the stuff that will never happen... its also easier on the eye!)
> +/* Get the CPU if the task is on it. */
> +static bool task_on_cpu(struct task_struct *t, int *cpu)
> +{
> + /*
> + * This is safe on x86 w/o barriers as the ordering of writing to
> + * task_cpu() and t->on_cpu is reverse to the reading here. The
> + * detection is inaccurate as tasks might move or schedule before
> + * the smp function call takes place. In such a case the function
> + * call is pointless, but there is no other side effect.
> + */
> + if (t->on_cpu) {
kernel/sched/core.c calls out that there can be two tasks on one CPU with this set.
(grep astute)
I think that means this series will falsely match the old task for a CPU while the
scheduler is running, and IPI it unnecessarily.
task_curr() is the helper that knows not to do this.
> + *cpu = task_cpu(t);
> +
> + return true;
> + }
> +
> + return false;
> +}
Thanks,
James
next prev parent reply other threads:[~2020-12-09 16:48 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-03 23:25 [PATCH 0/3] x86/resctrl: Fix a few issues in moving a task to a resource group Reinette Chatre
2020-12-03 23:25 ` [PATCH 1/3] x86/resctrl: Move setting task's active CPU in a mask into helpers Reinette Chatre
2020-12-07 18:29 ` Borislav Petkov
2020-12-07 21:24 ` Reinette Chatre
2020-12-08 9:49 ` Borislav Petkov
2020-12-08 16:35 ` Reinette Chatre
2020-12-09 16:47 ` James Morse [this message]
2020-12-10 0:21 ` Reinette Chatre
2020-12-03 23:25 ` [PATCH 2/3] x86/resctrl: Update PQR_ASSOC MSR synchronously when moving task to resource group Reinette Chatre
2020-12-09 16:51 ` James Morse
2020-12-10 0:22 ` Reinette Chatre
2020-12-11 20:46 ` Valentin Schneider
2020-12-14 18:41 ` Reinette Chatre
2020-12-16 17:41 ` Valentin Schneider
2020-12-16 18:26 ` Reinette Chatre
2020-12-17 10:39 ` Valentin Schneider
2020-12-03 23:25 ` [PATCH 3/3] x86/resctrl: Don't move a task to the same " Reinette Chatre
2020-12-11 20:46 ` [PATCH 0/3] x86/resctrl: Fix a few issues in moving a task to a " Valentin Schneider
2020-12-14 18:38 ` Reinette Chatre
2020-12-16 17:41 ` Valentin Schneider
2020-12-16 18:26 ` Reinette Chatre
2020-12-17 12:19 ` [PATCH 4/3] x86/intel_rdt: Apply READ_ONCE/WRITE_ONCE to task_struct .rmid & .closid Valentin Schneider
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