linux-kernel - Re: [RFC v2 PATCH 1/7] x86/resctrl: Add multiple tasks to the resctrl group at once

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Date:   Thu, 16 Feb 2023 14:27:05 -0800
From:   Fenghua Yu <fenghua.yu@...el.com>
To:     Babu Moger <babu.moger@....com>, <reinette.chatre@...el.com>
CC:     <tglx@...utronix.de>, <mingo@...hat.com>, <bp@...en8.de>,
        <dave.hansen@...ux.intel.com>, <x86@...nel.org>, <hpa@...or.com>,
        <corbet@....net>, <linux-kernel@...r.kernel.org>,
        <linux-doc@...r.kernel.org>, <eranian@...gle.com>,
        <peternewman@...gle.com>
Subject: Re: [RFC v2 PATCH 1/7] x86/resctrl: Add multiple tasks to the resctrl
 group at once

Hi, Babu,

On 2/2/23 13:46, Babu Moger wrote:
> The resctrl task assignment for MONITOR or CONTROL group needs to be
> done one at a time. For example:
> 
>    $mount -t resctrl resctrl /sys/fs/resctrl/
>    $mkdir /sys/fs/resctrl/clos1
>    $echo 123 > /sys/fs/resctrl/clos1/tasks
>    $echo 456 > /sys/fs/resctrl/clos1/tasks
>    $echo 789 > /sys/fs/resctrl/clos1/tasks
> 
> This is not user-friendly when dealing with hundreds of tasks.

Maybe add something like "poor performance due to syscall overhead...".

> 
> Improve the user experience by supporting the multiple task assignment
> in one command with the tasks separated by commas. For example:
> 
>    $echo 123,456,789 > /sys/fs/resctrl/clos1/tasks
> 
> Signed-off-by: Babu Moger <babu.moger@....com>
> ---
>   Documentation/x86/resctrl.rst          |    9 +++++++--
>   arch/x86/kernel/cpu/resctrl/rdtgroup.c |   24 +++++++++++++++++++++++-
>   2 files changed, 30 insertions(+), 3 deletions(-)
> 
> diff --git a/Documentation/x86/resctrl.rst b/Documentation/x86/resctrl.rst
> index 058257dc56c8..58b76fc75cb7 100644
> --- a/Documentation/x86/resctrl.rst
> +++ b/Documentation/x86/resctrl.rst
> @@ -292,13 +292,18 @@ All groups contain the following files:
>   "tasks":
>   	Reading this file shows the list of all tasks that belong to
>   	this group. Writing a task id to the file will add a task to the
> -	group. If the group is a CTRL_MON group the task is removed from
> +	group. Multiple tasks can be assigned together in one command by
> +	inputting the tasks separated by commas. Tasks will be assigned
> +	sequentially in the order it is provided. Failure while assigning
> +	the tasks will be aborted immediately and tasks next in the
> +	sequence will not be assigned. Users may need to retry them again.

May need to add "tasks before the failure are assigned...".

To retry movement, user needs to know which pid fails. So it's better
to add "last_command_status shows the failure pid and user can parse
it to retry assignment starting from the failure pid".

> +
> +	If the group is a CTRL_MON group the task is removed from
>   	whichever previous CTRL_MON group owned the task and also from
>   	any MON group that owned the task. If the group is a MON group,
>   	then the task must already belong to the CTRL_MON parent of this
>   	group. The task is removed from any previous MON group.
>   
> -
>   "cpus":
>   	Reading this file shows a bitmask of the logical CPUs owned by
>   	this group. Writing a mask to this file will add and remove
> diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> index e2c1599d1b37..13b7c5f3a27c 100644
> --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> @@ -683,16 +683,34 @@ static ssize_t rdtgroup_tasks_write(struct kernfs_open_file *of,
>   				    char *buf, size_t nbytes, loff_t off)
>   {
>   	struct rdtgroup *rdtgrp;
> +	char *pid_str;
>   	int ret = 0;
>   	pid_t pid;
>   
> -	if (kstrtoint(strstrip(buf), 0, &pid) || pid < 0)
> +	/* Valid input requires a trailing newline */
> +	if (nbytes == 0 || buf[nbytes - 1] != '\n')
>   		return -EINVAL;
> +
> +	buf[nbytes - 1] = '\0';
> +
>   	rdtgrp = rdtgroup_kn_lock_live(of->kn);
>   	if (!rdtgrp) {
>   		rdtgroup_kn_unlock(of->kn);
>   		return -ENOENT;
>   	}
> +
> +next:
> +	if (!buf || buf[0] == '\0')
> +		goto unlock;
> +
> +	pid_str = strim(strsep(&buf, ","));
> +
> +	if (kstrtoint(pid_str, 0, &pid) || pid < 0) {
> +		rdt_last_cmd_puts("Invalid pid value\n");

Better to add pid_str in failure info. Then user knows where the failure 
pid happens and can re-do the movement starting from the failed pid.

> +		ret = -EINVAL;
> +		goto unlock;
> +	}
> +
>   	rdt_last_cmd_clear();
>   
>   	if (rdtgrp->mode == RDT_MODE_PSEUDO_LOCKED ||
> @@ -703,6 +721,10 @@ static ssize_t rdtgroup_tasks_write(struct kernfs_open_file *of,
>   	}
>   
>   	ret = rdtgroup_move_task(pid, rdtgrp, of);
> +	if (ret)

May need to report "Failed at %d\n", pid;

> +		goto unlock;
> +	else
> +		goto next;
>   
>   unlock:
>   	rdtgroup_kn_unlock(of->kn);
> 
> 

Thanks.

-Fenghua