linux-kernel - Re: [RFC PATCH v1 00/11] Create fast idle path for short idle periods

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]

Date:   Mon, 17 Jul 2017 15:58:51 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     "Li, Aubrey" <aubrey.li@...ux.intel.com>
Cc:     paulmck@...ux.vnet.ibm.com, Andi Kleen <ak@...ux.intel.com>,
        Frederic Weisbecker <fweisbec@...il.com>,
        Christoph Lameter <cl@...ux.com>,
        Aubrey Li <aubrey.li@...el.com>, tglx@...utronix.de,
        len.brown@...el.com, rjw@...ysocki.net, tim.c.chen@...ux.intel.com,
        arjan@...ux.intel.com, yang.zhang.wz@...il.com, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v1 00/11] Create fast idle path for short idle periods

On Mon, Jul 17, 2017 at 09:24:51PM +0800, Li, Aubrey wrote:
> On 2017/7/14 12:05, Paul E. McKenney wrote:
> >
> > More specifically: rcu_needs_cpu(), rcu_prepare_for_idle(),
> > rcu_cleanup_after_idle(), rcu_eqs_enter(), rcu_eqs_enter_common(),
> > rcu_dynticks_eqs_enter(), do_nocb_deferred_wakeup(),
> > rcu_dynticks_task_enter(), rcu_eqs_exit(), rcu_eqs_exit_common(),
> > rcu_dynticks_task_exit(), rcu_dynticks_eqs_exit().
> >
> > The first three (rcu_needs_cpu(), rcu_prepare_for_idle(), and
> > rcu_cleanup_after_idle()) should not be significant unless you have
> > CONFIG_RCU_FAST_NO_HZ=y.  If you do, it would be interesting to learn
> > how often invoke_rcu_core() is invoked from rcu_prepare_for_idle()
> > and rcu_cleanup_after_idle(), as this can raise softirq.  Also
> > rcu_accelerate_cbs() and rcu_try_advance_all_cbs().
> >
> > Knowing which of these is causing the most trouble might help me
> > reduce the overhead in the current idle path.
> 
> I measured two cases, nothing notable found.

So skipping rcu_idle_{enter,exit}() is not in fact needed at all?