linux-kernel - Re: [RFC PATCH 24/24] sched/time: Introduce CLOCK_THREAD_DVFS

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Message-ID: <1c4d6e55-5440-4385-9a28-998da18af9bc@arm.com>
Date: Mon, 19 Aug 2024 12:11:03 +0100
From: Christian Loehle <christian.loehle@....com>
To: Peter Zijlstra <peterz@...radead.org>, mingo@...hat.com,
 juri.lelli@...hat.com, vincent.guittot@...aro.org, dietmar.eggemann@....com,
 rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
 vschneid@...hat.com, linux-kernel@...r.kernel.org
Cc: kprateek.nayak@....com, wuyun.abel@...edance.com,
 youssefesmat@...omium.org, tglx@...utronix.de, efault@....de
Subject: Re: [RFC PATCH 24/24] sched/time: Introduce CLOCK_THREAD_DVFS_ID

On 7/27/24 11:27, Peter Zijlstra wrote:
> In order to measure thread time in a DVFS world, introduce
> CLOCK_THREAD_DVFS_ID -- a copy of CLOCK_THREAD_CPUTIME_ID that slows
> down with both DVFS scaling and CPU capacity.
> 
> The clock does *NOT* support setting timers.
> 
> Useful for both SCHED_DEADLINE and the newly introduced
> sched_attr::sched_runtime usage for SCHED_NORMAL.
> 

How will this look like in practice then?
Is it up to userspace to adjust sched_runtime to capacity/dvfs
accordingly every time it changes? I guess not.
Will sched_attr::sched_runtime be for CPUCLOCK_DVFS by default?
I assume that would be a uapi change?
Do we need an additional flag in sched_attr to specify the clock
to be measured against?

> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> ---
>  include/linux/posix-timers_types.h |    5 ++--
>  include/linux/sched.h              |    1 
>  include/linux/sched/cputime.h      |    3 ++
>  include/uapi/linux/time.h          |    1 
>  kernel/sched/core.c                |   40 +++++++++++++++++++++++++++++++++++++
>  kernel/sched/fair.c                |    8 +++++--
>  kernel/time/posix-cpu-timers.c     |   16 +++++++++++++-
>  kernel/time/posix-timers.c         |    1 
>  kernel/time/posix-timers.h         |    1 
>  9 files changed, 71 insertions(+), 5 deletions(-)
> 
> --- a/include/linux/posix-timers_types.h
> +++ b/include/linux/posix-timers_types.h
> @@ -13,9 +13,9 @@
>   *
>   * Bit 2 indicates whether a cpu clock refers to a thread or a process.
>   *
> - * Bits 1 and 0 give the type: PROF=0, VIRT=1, SCHED=2, or FD=3.
> + * Bits 1 and 0 give the type: PROF=0, VIRT=1, SCHED=2, or DVSF=3

s/DVSF/DVFS

> [snip]