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From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
To: Chris Lameter <cl@linux.com>
Cc: Jann Horn <jannh@google.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	Joel Fernandes <joelaf@google.com>,
	Ingo Molnar <mingo@redhat.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Dave Watson <davejwatson@fb.com>,
	Will Deacon <will.deacon@arm.com>, shuah <shuah@kernel.org>,
	Andi Kleen <andi@firstfloor.org>,
	linux-kselftest <linux-kselftest@vger.kernel.org>,
	"H. Peter Anvin" <hpa@zytor.com>,
	Russell King <linux@arm.linux.org.uk>,
	Michael Kerrisk <mtk.manpages@gmail.com>,
	Paul <paulmck@linux.vnet.ibm.com>, Paul Turner <pjt@google.com>,
	Boqun Feng <boqun.feng@gmail.com>,
	Josh Triplett <josh@joshtriplett.org>,
	rostedt <rostedt@goodmis.org>, Ben Maurer <bmaurer@fb.com>,
	linux-api <linux-api@vger.kernel.org>,
	Andy Lutomirski <luto@amacapital.net>
Subject: Re: [RFC PATCH v1] pin_on_cpu: Introduce thread CPU pinning system call
Date: Tue, 21 Jan 2020 20:11:08 -0500 (EST)	[thread overview]
Message-ID: <1648013936.596672.1579655468604.JavaMail.zimbra@efficios.com> (raw)
In-Reply-To: <alpine.DEB.2.21.2001212141590.1231@www.lameter.com>

----- On Jan 21, 2020, at 4:44 PM, Chris Lameter cl@linux.com wrote:

> These scenarios are all pretty complex and will be difficult to understand
> for the user of these APIs.
> 
> I think the easiest solution (and most comprehensible) is for the user
> space process that does per cpu operations to get some sort of signal. If
> its not able to handle that then terminate it. The code makes a basic
> assumption after all that the process is running on a specific cpu. If
> this is no longer the case then its better to abort if the process cannot
> handle moving to a different processor.

The point of pin_on_cpu() is to allow threads to access per-cpu data
structures belonging to a given CPU even if they cannot run on that
CPU (because it is offline).

I am not sure what scenario your signal delivery proposal aims to cover.

Just to try to put this into the context of a specific scenario to see
if I understand your point, is the following what you have in mind ?

1. Thread A issues pin_on_cpu(5),
2. Thread B issues sched_setaffinity removing cpu 5 from thread A's
   affinity mask,
3. Noticing that it would generate an invalid combination, rather than
   failing sched_setaffinity, it would send a SIGSEGV (or other) signal
   to thread A.

Or so you have something entirely different in mind ?

Thanks,

Mathieu

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com

  reply	other threads:[~2020-01-22  1:11 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-01-21 16:03 [RFC PATCH v1] pin_on_cpu: Introduce thread CPU pinning system call Mathieu Desnoyers
2020-01-21 17:20 ` Jann Horn
2020-01-21 19:47   ` Mathieu Desnoyers
2020-01-21 20:35     ` Jann Horn
2020-01-21 21:18       ` Mathieu Desnoyers
2020-01-21 21:44         ` Christopher Lameter
2020-01-22  1:11           ` Mathieu Desnoyers [this message]
2020-01-23  7:53             ` H. Peter Anvin
2020-01-23  8:19               ` Florian Weimer
2020-01-27 19:39                 ` Mathieu Desnoyers
2020-01-30 11:10                   ` Florian Weimer
2020-02-14 16:54                     ` Mathieu Desnoyers
2020-01-22  8:23         ` Jann Horn
2020-01-22 15:48 Jan Ziak
     [not found] <CAODFU0rTLmb-Ph_n1EHaZmdOAjsa6Jmx=3zkuT8LH3No=sOk5w@mail.gmail.com>
2020-01-22 17:16 ` Mathieu Desnoyers

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