linux-kernel.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Frederic Weisbecker <fweisbec@gmail.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
	linux-kernel@vger.kernel.org, mingo@elte.hu,
	laijs@cn.fujitsu.com, dipankar@in.ibm.com,
	akpm@linux-foundation.org, mathieu.desnoyers@polymtl.ca,
	josh@joshtriplett.org, niv@us.ibm.com, tglx@linutronix.de,
	rostedt@goodmis.org, Valdis.Kletnieks@vt.edu,
	dhowells@redhat.com, eric.dumazet@gmail.com, darren@dvhart.com,
	sbw@mit.edu, patches@linaro.org,
	Alessio Igor Bogani <abogani@kernel.org>,
	Avi Kivity <avi@redhat.com>, Chris Metcalf <cmetcalf@tilera.com>,
	Christoph Lameter <cl@linux.com>,
	Geoff Levand <geoff@infradead.org>,
	Gilad Ben Yossef <gilad@benyossef.com>,
	Hakan Akkan <hakanakkan@gmail.com>,
	"H. Peter Anvin" <hpa@zytor.com>, Ingo Molnar <mingo@kernel.org>,
	Kevin Hilman <khilman@ti.com>,
	Max Krasnyansky <maxk@qualcomm.com>,
	Stephen Hemminger <shemminger@vyatta.com>,
	Sven-Thorsten Dietrich <thebigcorporation@gmail.com>
Subject: Re: [PATCH tip/core/rcu 11/26] rcu: Exit RCU extended QS on user preemption
Date: Wed, 12 Sep 2012 15:54:50 +0200	[thread overview]
Message-ID: <20120912135420.GB17139@somewhere.redhat.com> (raw)
In-Reply-To: <1347454360.15764.27.camel@twins>

On Wed, Sep 12, 2012 at 02:52:40PM +0200, Peter Zijlstra wrote:
> On Wed, 2012-09-12 at 14:41 +0200, Peter Zijlstra wrote:
> 
> > We could of course mandate that all remote wakeups to special nohz cpus
> > get queued. That would just leave us with RCU and it would simply not
> > send resched IPIs to extended quiescent CPUs anyway, right?
> > 
> > So at that point all return to user schedule() calls have nr_running > 1
> > and the tick is running and RCU is not in extended quiescent state.
> > Since either we had nr_running > 1 and pre and post state are the same,
> > or we had nr_running == 1 and we just got a fresh wakeup pushing it to
> > 2, the wakeup will have executed on our cpu and have re-started the tick
> > and kicked RCU into active gear again.
> > 
> > We cannot hit return to user schedule() with nr_running == 0, simply
> > because in that case there's no userspace to return to, only the idle
> > thread and that's very much not userspace :-)
> > 
> > Hmm ?
> 
> Crap.. this will screw over -rt, since the wakeups batch the IPI can
> take forever so we had to disable this.

I don't know that part of -rt. Probably we can deal with that later once
we have some upstream code in place?

> 
> Bugger it.. I so detest this patch.

  reply	other threads:[~2012-09-12 13:55 UTC|newest]

Thread overview: 73+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2012-08-30 21:05 [PATCH tip/core/rcu 0/26] idle-related changes Paul E. McKenney
2012-08-30 21:05 ` [PATCH tip/core/rcu 01/26] rcu: New rcu_user_enter() and rcu_user_exit() APIs Paul E. McKenney
2012-08-30 21:05   ` [PATCH tip/core/rcu 02/26] rcu: New rcu_user_enter_irq() and rcu_user_exit_irq() APIs Paul E. McKenney
2012-08-31 19:13     ` Josh Triplett
2012-08-31 19:54       ` Frederic Weisbecker
2012-08-31 21:38         ` Josh Triplett
2012-08-30 21:05   ` [PATCH tip/core/rcu 03/26] rcu: Make RCU_FAST_NO_HZ handle adaptive ticks Paul E. McKenney
2012-08-31 23:40     ` Josh Triplett
2012-08-30 21:05   ` [PATCH tip/core/rcu 04/26] rcu: Settle config for userspace extended quiescent state Paul E. McKenney
2012-08-31 23:44     ` Josh Triplett
2012-09-05  0:34       ` Paul E. McKenney
2012-09-05  0:46         ` Josh Triplett
2012-09-10 21:35           ` Frederic Weisbecker
2012-08-30 21:05   ` [PATCH tip/core/rcu 05/26] rcu: Allow rcu_user_enter()/exit() to nest Paul E. McKenney
2012-08-31 23:45     ` Josh Triplett
2012-08-30 21:05   ` [PATCH tip/core/rcu 06/26] rcu: Ignore userspace extended quiescent state by default Paul E. McKenney
2012-08-31 23:46     ` Josh Triplett
2012-08-30 21:05   ` [PATCH tip/core/rcu 07/26] rcu: Switch task's syscall hooks on context switch Paul E. McKenney
2012-08-31 23:48     ` Josh Triplett
2012-08-30 21:05   ` [PATCH tip/core/rcu 08/26] x86: Syscall hooks for userspace RCU extended QS Paul E. McKenney
2012-08-31 23:59     ` Josh Triplett
2012-09-10 21:30       ` Frederic Weisbecker
2012-08-30 21:05   ` [PATCH tip/core/rcu 09/26] x86: Exception " Paul E. McKenney
2012-08-31 23:51     ` Josh Triplett
2012-08-30 21:05   ` [PATCH tip/core/rcu 10/26] rcu: Exit RCU extended QS on kernel preemption after irq/exception Paul E. McKenney
2012-08-31 23:51     ` Josh Triplett
2012-09-06 16:52     ` Peter Zijlstra
2012-09-10 20:31       ` Frederic Weisbecker
2012-08-30 21:05   ` [PATCH tip/core/rcu 11/26] rcu: Exit RCU extended QS on user preemption Paul E. McKenney
2012-08-31 23:52     ` Josh Triplett
2012-09-06 17:02     ` Peter Zijlstra
2012-09-06 17:13       ` Peter Zijlstra
2012-09-10 20:26         ` Frederic Weisbecker
2012-09-12  9:33           ` Peter Zijlstra
2012-09-12 12:06             ` Frederic Weisbecker
2012-09-12 12:41               ` Peter Zijlstra
2012-09-12 12:52                 ` Peter Zijlstra
2012-09-12 13:54                   ` Frederic Weisbecker [this message]
2012-09-12 14:09                     ` Peter Zijlstra
2012-09-12 13:52                 ` Frederic Weisbecker
2012-09-12 15:21                 ` Paul E. McKenney
2012-08-30 21:05   ` [PATCH tip/core/rcu 12/26] x86: Use the new schedule_user API on userspace preemption Paul E. McKenney
2012-08-31 23:53     ` Josh Triplett
2012-08-30 21:05   ` [PATCH tip/core/rcu 13/26] x86: Exit RCU extended QS on notify resume Paul E. McKenney
2012-08-31 23:54     ` Josh Triplett
2012-08-30 21:05   ` [PATCH tip/core/rcu 14/26] rcu: Userspace RCU extended QS selftest Paul E. McKenney
2012-08-31 23:54     ` Josh Triplett
2012-08-30 21:05   ` [PATCH tip/core/rcu 15/26] alpha: Fix preemption handling in idle loop Paul E. McKenney
2012-08-31 23:55     ` Josh Triplett
2012-08-30 21:05   ` [PATCH tip/core/rcu 16/26] alpha: Add missing RCU idle APIs on " Paul E. McKenney
2012-09-01  0:00     ` Josh Triplett
2012-08-30 21:05   ` [PATCH tip/core/rcu 17/26] cris: " Paul E. McKenney
2012-09-01  0:01     ` Josh Triplett
2012-08-30 21:05   ` [PATCH tip/core/rcu 18/26] frv: " Paul E. McKenney
2012-09-01  0:01     ` Josh Triplett
2012-08-30 21:05   ` [PATCH tip/core/rcu 19/26] h8300: " Paul E. McKenney
2012-09-01  0:02     ` Josh Triplett
2012-08-30 21:05   ` [PATCH tip/core/rcu 20/26] m32r: " Paul E. McKenney
2012-09-01  0:02     ` Josh Triplett
2012-08-30 21:05   ` [PATCH tip/core/rcu 21/26] m68k: " Paul E. McKenney
2012-09-01  0:02     ` Josh Triplett
2012-08-30 21:05   ` [PATCH tip/core/rcu 22/26] mn10300: " Paul E. McKenney
2012-09-01  0:03     ` Josh Triplett
2012-08-30 21:05   ` [PATCH tip/core/rcu 23/26] parisc: " Paul E. McKenney
2012-09-01  0:03     ` Josh Triplett
2012-08-30 21:05   ` [PATCH tip/core/rcu 24/26] score: " Paul E. McKenney
2012-09-01  0:04     ` Josh Triplett
2012-08-30 21:05   ` [PATCH tip/core/rcu 25/26] xtensa: " Paul E. McKenney
2012-09-01  0:05     ` Josh Triplett
2012-08-30 21:05   ` [PATCH tip/core/rcu 26/26] ia64: " Paul E. McKenney
2012-09-01  0:05     ` Josh Triplett
2012-08-31 19:07   ` [PATCH tip/core/rcu 01/26] rcu: New rcu_user_enter() and rcu_user_exit() APIs Josh Triplett
2012-09-05  1:04     ` Paul E. McKenney

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20120912135420.GB17139@somewhere.redhat.com \
    --to=fweisbec@gmail.com \
    --cc=Valdis.Kletnieks@vt.edu \
    --cc=abogani@kernel.org \
    --cc=akpm@linux-foundation.org \
    --cc=avi@redhat.com \
    --cc=cl@linux.com \
    --cc=cmetcalf@tilera.com \
    --cc=darren@dvhart.com \
    --cc=dhowells@redhat.com \
    --cc=dipankar@in.ibm.com \
    --cc=eric.dumazet@gmail.com \
    --cc=geoff@infradead.org \
    --cc=gilad@benyossef.com \
    --cc=hakanakkan@gmail.com \
    --cc=hpa@zytor.com \
    --cc=josh@joshtriplett.org \
    --cc=khilman@ti.com \
    --cc=laijs@cn.fujitsu.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=mathieu.desnoyers@polymtl.ca \
    --cc=maxk@qualcomm.com \
    --cc=mingo@elte.hu \
    --cc=mingo@kernel.org \
    --cc=niv@us.ibm.com \
    --cc=patches@linaro.org \
    --cc=paulmck@linux.vnet.ibm.com \
    --cc=peterz@infradead.org \
    --cc=rostedt@goodmis.org \
    --cc=sbw@mit.edu \
    --cc=shemminger@vyatta.com \
    --cc=tglx@linutronix.de \
    --cc=thebigcorporation@gmail.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body. 
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).