From: nsaenzju@redhat.com
To: Marcelo Tosatti <mtosatti@redhat.com>
Cc: Frederic Weisbecker <frederic@kernel.org>,
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: Wed, 28 Jul 2021 19:08:45 +0200 [thread overview]
Message-ID: <441d94dbd93443839d31fdfe5f6048de35b0d7b0.camel@redhat.com> (raw)
In-Reply-To: <20210728131610.GA11900@fuller.cnet>
On Wed, 2021-07-28 at 10:16 -0300, Marcelo Tosatti wrote:
> > For example, let's say we introduce ISOL_F_QUIESCE_DEFER_TLB_FLUSH, this will
> > defer relatively short IPIs on isolated CPUs in exchange for a longer flush
> > whenever we enter the kernel (syscall, IRQs, NMI, etc...).
>
> Why the flush has to be longer when you enter the kernel?
What I had in mind was cost of rapid partial flushes (IPIs) vs full flushes on
entry, although I haven't really measured anything so the extra latency cost
might as well be zero.
> ISOL_F_QUIESCE_DEFER_TLB_FLUSH might collapse multiple IPIs
> into a single IPI, so the behaviour might be beneficial
> for "standard" types of application as well.
>
> > A latency sensitive
> > application might be OK with the former but not with the latter.
>
> Two alternatives:
>
> 1) The pattern above, where particular subsystems that might interrupt
> the kernel are enabled automatically if the kernel supports it.
>
> Pros:
> Applications which implement this only need to be changed once,
> and can benefit from new kernel features.
>
> Applications can disable particular features if they turn
> out to be problematic.
>
> Cons:
> New features might break applications.
>
> 2) Force applications to enable each new feature individually.
>
> Pros: Won't cause regressions, kernel behaviour is explicitly
> controlled by userspace.
>
> Cons: Apps won't benefit from new features automatically.
>
> ---
>
> It seems to me 1) is preferred. Can also add a sysfs control to
> have a "default_isolation_feature" flag, which can be changed
> by a sysadmin in case a new feature is undesired.
>
> Thoughts?
I'd still take option 2. Nitesh has a very good point, latency requirements are
hit or miss. What's the benefit of enabling new features on an already valid
application vs the potential regression?
That said I see value in providing means for users that want all
features/modes, but it should be an through an explicit action on their part.
--
Nicolás Sáenz
next prev parent reply other threads:[~2021-07-28 17:09 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
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 [this message]
[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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