linux-kernel - Re: [RFC PATCH v2] membarrier: expedited private command

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <20170801233203.GO3730@linux.vnet.ibm.com>
Date:   Tue, 1 Aug 2017 16:32:03 -0700
From:   "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Nicholas Piggin <npiggin@...il.com>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Boqun Feng <boqun.feng@...il.com>,
        Andrew Hunter <ahh@...gle.com>,
        maged michael <maged.michael@...il.com>,
        gromer <gromer@...gle.com>, Avi Kivity <avi@...lladb.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Palmer Dabbelt <palmer@...belt.com>,
        Dave Watson <davejwatson@...com>
Subject: Re: [RFC PATCH v2] membarrier: expedited private command

On Tue, Aug 01, 2017 at 04:16:54PM +0200, Peter Zijlstra wrote:
> On Tue, Aug 01, 2017 at 06:23:09AM -0700, Paul E. McKenney wrote:
> > On Tue, Aug 01, 2017 at 12:22:03PM +0200, Peter Zijlstra wrote:
> > 
> > [ . . . ]
> > 
> > > As to scheduler IPIs, those are limited to the CPUs the user is limited
> > > to and are rate limited by the wakeup-latency of the tasks. After all,
> > > all the time a task is runnable but not running, wakeups are no-ops.
> > 
> > Can't that wakeup-latency limitation be overcome by a normal user simply
> > by having lots of tasks to wake up, which then go back to sleep almost
> > immediately?  Coupled with very a low-priority CPU-bound task on each CPU?
> 
> Let me put it like this; there is no way to cause more interference
> using IPIs then there is simply running while(1) loops ;-)

Very good, that does give us some guidance, give or take context switches
happening during the IPI latency window.  ;-)

							Thanx, Paul