From: Steven Rostedt <rostedt@goodmis.org>
To: Song Chen <chensong_2000@189.cn>
Cc: mingo@redhat.com, peterz@infradead.org, juri.lelli@redhat.com,
vincent.guittot@linaro.org, dietmar.eggemann@arm.com,
bsegall@google.com, mgorman@suse.de, bristot@redhat.com,
vschneid@redhat.com, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] kernel/sched/core: adjust rt_priority accordingly when prio is changed
Date: Wed, 1 Feb 2023 10:56:03 -0500 [thread overview]
Message-ID: <20230201105603.1d377866@gandalf.local.home> (raw)
In-Reply-To: <1675245680-2811-1-git-send-email-chensong_2000@189.cn>
On Wed, 1 Feb 2023 18:01:20 +0800
Song Chen <chensong_2000@189.cn> wrote:
> When a high priority process is acquiring a rtmutex which is held by a
> low priority process, the latter's priority will be boosted up by calling
> rt_mutex_setprio->__setscheduler_prio.
>
> However, p->prio is changed but p->rt_priority is not, as a result, the
> equation between prio and rt_priority is broken, which is:
>
> prio = MAX_RT_PRIO - 1 - rt_priority
>
> It's confusing to the user when it calls sched_getparam, which only
> returns rt_priority.
If it is boosted, then that's an internal implementation and not the real
priority of the task. It should not be exposed to a user interface. In
fact, there's discussion of implementing a "proxy" algorithm which will
make what the "priority" of a task is even more complicated when acquiring
mutexes.
>
> This patch addresses this issue by adjusting rt_priority according to
> the new value of prio, what's more, it also returns normal_prio for
> CFS processes instead of just a zero.
The comment above sched_getparam() is:
/**
* sys_sched_getparam - get the RT priority of a thread
* @pid: the pid in question.
* @param: structure containing the RT priority.
*
* Return: On success, 0 and the RT priority is in @param. Otherwise, an error
* code.
*/
So returning the nice value is incorrect. If anything, perhaps it should
return -EINVAL if the task is not an RT task?
-- Steve
>
> Signed-off-by: Song Chen <chensong_2000@189.cn>
> ---
prev parent reply other threads:[~2023-02-01 15:56 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-02-01 10:01 [PATCH] kernel/sched/core: adjust rt_priority accordingly when prio is changed Song Chen
2023-02-01 15:56 ` Steven Rostedt [this message]
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