linux-kernel - Re: [PATCH v1 1/6] x86/resctrl: Move __resctrl_sched

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Date: Mon, 8 Apr 2024 14:41:22 -0700
From: Peter Newman <peternewman@...gle.com>
To: Reinette Chatre <reinette.chatre@...el.com>
Cc: Fenghua Yu <fenghua.yu@...el.com>, James Morse <james.morse@....com>, 
	Stephane Eranian <eranian@...gle.com>, Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, 
	Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org, 
	"H. Peter Anvin" <hpa@...or.com>, Peter Zijlstra <peterz@...radead.org>, Juri Lelli <juri.lelli@...hat.com>, 
	Vincent Guittot <vincent.guittot@...aro.org>, Dietmar Eggemann <dietmar.eggemann@....com>, 
	Steven Rostedt <rostedt@...dmis.org>, Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>, 
	Daniel Bristot de Oliveira <bristot@...hat.com>, Valentin Schneider <vschneid@...hat.com>, 
	Uros Bizjak <ubizjak@...il.com>, Mike Rapoport <rppt@...nel.org>, 
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>, 
	Rick Edgecombe <rick.p.edgecombe@...el.com>, Xin Li <xin3.li@...el.com>, 
	Babu Moger <babu.moger@....com>, Shaopeng Tan <tan.shaopeng@...itsu.com>, 
	Maciej Wieczor-Retman <maciej.wieczor-retman@...el.com>, Jens Axboe <axboe@...nel.dk>, 
	Christian Brauner <brauner@...nel.org>, Oleg Nesterov <oleg@...hat.com>, 
	Andrew Morton <akpm@...ux-foundation.org>, Tycho Andersen <tandersen@...flix.com>, 
	Nicholas Piggin <npiggin@...il.com>, Beau Belgrave <beaub@...ux.microsoft.com>, 
	"Matthew Wilcox (Oracle)" <willy@...radead.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 1/6] x86/resctrl: Move __resctrl_sched_in() out-of-line

Hi Reinette,

On Mon, Apr 8, 2024 at 1:59 PM Reinette Chatre
<reinette.chatre@...el.com> wrote:
>
> Hi Peter,
>
> On 4/8/2024 12:05 PM, Peter Newman wrote:
> > Hi Reinette,
> >
> > On Sun, Apr 7, 2024 at 12:21 PM Reinette Chatre
> > <reinette.chatre@...el.com> wrote:
> >>
> >> I think this needs more thought. rdt_enable_key is x86 specific now and should not
> >> be in the fs code. Every architecture will have its own task switch code, with
> >> __resctrl_sched_in() belonging to x86 and thus not something to be directly called
> >> from the fs code.
> >
> > I think we will need to discuss whether __resctrl_sched_in() is really
> > arch or FS code following the changes in this series. This series
> > removes the explicit MSR access and James has already provided inline
>
> Indeed, I missed how resctrl_arch_update_cpu() introduced in
> "x86/resctrl: Abstract PQR_ASSOC from generic code" results in
> __resctrl_sched_in() being architecture agnostic.
>
> (sidenotes ...  it is not obvious to me why resctrl_arch_update_cpu()
> is not consistently used, for example, in clear_closid_rmid(),
> and it also seems a better candidate to be inline within
> arch/x86/include/asm/resctrl.h)

I must have renamed resctrl_pqr_state to resctrl_cpu_state after I
last looked over clear_closid_rmid(). Now looking at the function
again, it seems clearly portable now and should definitely use
resctrl_arch_update_cpu(). I need to look over the accesses to
resctrl_cpu_state again to reconsider whether they're
architecture-dependent.

>
> > wrappers for the mon and alloc enable keys[1], so I can only assume
> > they are architecture-independent in concept.
>
> The wrappers are intended to be architecture-independent, but the keys
> are architecture dependent. Quoting the commit you linked to:
> "This means other architectures don't have to mirror the static keys"

The static keys seem to exist mainly for the benefit of
__resctrl_sched_in(), so if it becomes architecture-agnostic, I think
it would make sense for the static keys to move into the FS code with
it. I don't see any other usage of these keys in the code that
remained under arch/x86 on James' latest series.

-Peter