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

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Message-ID: <090d80c5-47ad-c152-27cc-81019aa5daef@amd.com>
Date:   Fri, 17 Feb 2023 09:05:55 -0600
From:   "Moger, Babu" <bmoger@....com>
To:     Fenghua Yu <fenghua.yu@...el.com>, 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 Fenghua,

On 2/16/2023 4:27 PM, Fenghua Yu wrote:
> 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...".
Ok. Sure
>
>>
>> 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...".
Sure.
>
> 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".
Sure.
>
>> +
>> +    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.

ok.

>
>> +        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;

Ok. Dont want to overwrite the last command status. I may need to update 
it with pid. Will check on this.

thanks

Babu

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