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From: Marcelo Tosatti <mtosatti@redhat.com>
To: Frederic Weisbecker <frederic@kernel.org>
Cc: nsaenzju@redhat.com, linux-kernel@vger.kernel.org,
	Nitesh Lal <nilal@redhat.com>, Christoph Lameter <cl@linux.com>,
	Juri Lelli <juri.lelli@redhat.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Alex Belits <abelits@marvell.com>, Peter Xu <peterx@redhat.com>,
	Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [patch 1/4] add basic task isolation prctl interface
Date: Tue, 27 Jul 2021 11:52:09 -0300	[thread overview]
Message-ID: <20210727145209.GA518735@fuller.cnet> (raw)
In-Reply-To: <20210727130930.GB283787@lothringen>

On Tue, Jul 27, 2021 at 03:09:30PM +0200, Frederic Weisbecker wrote:
> On Tue, Jul 27, 2021 at 02:38:15PM +0200, nsaenzju@redhat.com wrote:
> > Hi Marcelo,
> > 
> > On Tue, 2021-07-27 at 08:00 -0300, Marcelo Tosatti wrote:
> > OK, sorry if I'm being thick, but what is the benefit of having a distincnt
> > PR_ISOL_MODE instead expressing everything as PR_ISOL_FEATURES.
> > 
> >   PR_ISOL_MODE_NONE == Empty PR_ISOL_FEATURES bitmap
> > 
> >   PR_ISOL_MODE_NORMAL == Bitmap of commonly used PR_ISOL_FEATURES
> >   			      (we could introduce a define)
> > 
> >   PR_ISOL_MODE_NORMAL+PR_ISOL_VSYSCALLS == Custom bitmap
> > 
> > Other than that, my rationale is that if you extend PR_ISOL_MODE_NORMAL's
> > behaviour as new features are merged, wouldn't you be potentially breaking
> > userspace (i.e. older applications might not like the new default)?
> 
> I agree with Nicolas, and that was Thomas request too.
> Let's leave policy implementation to userspace and take
> only the individual isolation features to the kernel.
> 
> CPU/Task isolation is a relatively young feature and many users don't
> communicate much about their needs. We don't know exactly how finegrained
> the ABI will need to be so let's not make too many high level assumptions.
> 
> It's easy for userspace to set all isolation bits by itself.
> 
> Besides, those bits will be implemented one by one over time, this
> means that a prctl() bit saying "isolate everything" will have a different
> behaviour as those features get integrated. And we really want well defined
> behaviours.
> 
> Thanks.
> 
> 

OK, how about this:

...

The meaning of isolated is specified as follows:

Isolation features
==================

- prctl(PR_ISOL_GET, ISOL_SUP_FEATURES, 0, 0, 0) returns the supported
features as a return value.

- prctl(PR_ISOL_SET, ISOL_FEATURES, bitmask, 0, 0) enables the features in
the bitmask.

- prctl(PR_ISOL_GET, ISOL_FEATURES, 0, 0, 0) returns the currently
enabled features.

The supported features are:

ISOL_F_QUIESCE_ON_URET: quiesce deferred actions on return to userspace.
----------------------

Quiescing of different actions can be performed on return to userspace.

- prctl(PR_ISOL_GET, PR_ISOL_SUP_QUIESCE_CFG, 0, 0, 0) returns
the supported actions to be quiesced.

- prctl(PR_ISOL_SET, PR_ISOL_QUIESCE_CFG, quiesce_bitmask, 0, 0) returns
the currently supported actions to be quiesced.

- prctl(PR_ISOL_GET, PR_ISOL_QUIESCE_CFG, 0, 0, 0) returns
the currently enabled actions to be quiesced.

#define ISOL_F_QUIESCE_VMSTAT_SYNC      (1<<0)
#define ISOL_F_QUIESCE_NOHZ_FULL        (1<<1)
#define ISOL_F_QUIESCE_DEFER_TLB_FLUSH  (1<<2)
...


  reply	other threads:[~2021-07-27 14:52 UTC|newest]

Thread overview: 26+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-27 10:38 [patch 0/4] prctl task isolation interface and vmstat sync Marcelo Tosatti
2021-07-27 10:38 ` [patch 1/4] add basic task isolation prctl interface Marcelo Tosatti
2021-07-27 10:48   ` nsaenzju
2021-07-27 11:00     ` Marcelo Tosatti
2021-07-27 12:38       ` nsaenzju
2021-07-27 13:06         ` Marcelo Tosatti
2021-07-27 13:08           ` Marcelo Tosatti
2021-07-27 13:09         ` Frederic Weisbecker
2021-07-27 14:52           ` Marcelo Tosatti [this message]
2021-07-27 23:45             ` Frederic Weisbecker
2021-07-28  9:37               ` Marcelo Tosatti
2021-07-28 11:45                 ` Frederic Weisbecker
2021-07-28 13:21                   ` Marcelo Tosatti
2021-07-28 21:22                     ` Frederic Weisbecker
2021-07-28 11:55                 ` nsaenzju
2021-07-28 13:16                   ` Marcelo Tosatti
     [not found]                     ` <CAFki+LkQwoqVTKmgnwLQQM8ua-ixbLp8i+jUT6xF15k6X=89mw@mail.gmail.com>
2021-07-28 16:21                       ` Marcelo Tosatti
2021-07-28 17:08                     ` nsaenzju
     [not found]                 ` <CAFki+LmHeXmSFze8YEHFNbYA5hLEtnZyk37Yjf-eyOuKa8Os4w@mail.gmail.com>
2021-07-28 16:17                   ` Marcelo Tosatti
2021-07-27 10:38 ` [patch 2/4] task isolation: sync vmstats on return to userspace Marcelo Tosatti
2021-07-27 10:38 ` [patch 3/4] mm: vmstat: move need_update Marcelo Tosatti
2021-07-27 10:38 ` [patch 4/4] mm: vmstat_refresh: avoid queueing work item if cpu stats are clean Marcelo Tosatti
2021-07-30 20:18 [patch 0/4] extensible prctl task isolation interface and vmstat sync (v2) Marcelo Tosatti
2021-07-30 20:18 ` [patch 1/4] add basic task isolation prctl interface Marcelo Tosatti
     [not found]   ` <CAFki+Lnf0cs62Se0aPubzYxP9wh7xjMXn7RXEPvrmtBdYBrsow@mail.gmail.com>
2021-07-31  0:49     ` Marcelo Tosatti
2021-07-31  7:47   ` kernel test robot
     [not found]   ` <CAFki+LkQVQOe+5aNEKWDvLdnjWjxzKWOiqOvBZzeuPWX+G=XgA@mail.gmail.com>
2021-08-02 14:16     ` Marcelo Tosatti

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