From: Andrea Parri <parri.andrea@gmail.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
linux-kernel <linux-kernel@vger.kernel.org>,
Ingo Molnar <mingo@kernel.org>,
Lai Jiangshan <jiangshanlai@gmail.com>,
dipankar <dipankar@in.ibm.com>,
Andrew Morton <akpm@linux-foundation.org>,
Josh Triplett <josh@joshtriplett.org>,
Thomas Gleixner <tglx@linutronix.de>,
rostedt <rostedt@goodmis.org>,
David Howells <dhowells@redhat.com>,
Eric Dumazet <edumazet@google.com>, fweisbec <fweisbec@gmail.com>,
Oleg Nesterov <oleg@redhat.com>,
Boqun Feng <boqun.feng@gmail.com>, Andrew Hunter <ahh@google.com>,
maged michael <maged.michael@gmail.com>,
gromer <gromer@google.com>, Avi Kivity <avi@scylladb.com>,
Benjamin Herrenschmidt <benh@kernel.crashing.org>
Subject: Re: [PATCH tip/core/rcu 1/3] membarrier: Provide register expedited private command
Date: Sat, 7 Oct 2017 17:10:04 +0200 [thread overview]
Message-ID: <20171007151004.GA3874@andrea> (raw)
In-Reply-To: <20171006083219.asdpl5w4pl6hedcd@hirez.programming.kicks-ass.net>
On Fri, Oct 06, 2017 at 10:32:19AM +0200, Peter Zijlstra wrote:
> > AFAIU the scheduler rq->lock is held while preemption is disabled.
> > synchronize_sched() is used here to ensure that all pre-existing
> > preempt-off critical sections have completed.
> >
> > So saying that we use synchronize_sched() to synchronize with rq->lock
> > would be stretching the truth a bit. It's actually only true because the
> > scheduler holding the rq->lock is surrounded by a preempt-off
> > critical section.
>
> No, rq->lock is sufficient, note that rq->lock is a raw_spinlock_t which
> implies !preempt. Yes, we also surround the rq->lock usage with a
> slightly larger preempt_disable() section but that's not in fact
> required for this.
That's what it is, according to the current sources: we seemed to agree that
a preempt-off critical section is what we rely on here and that the start of
this critical section is not marked by that raw_spin_lock.
Andrea
WARNING: multiple messages have this Message-ID (diff)
From: Andrea Parri <parri.andrea@gmail.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
linux-kernel <linux-kernel@vger.kernel.org>,
Ingo Molnar <mingo@kernel.org>,
Lai Jiangshan <jiangshanlai@gmail.com>,
dipankar <dipankar@in.ibm.com>,
Andrew Morton <akpm@linux-foundation.org>,
Josh Triplett <josh@joshtriplett.org>,
Thomas Gleixner <tglx@linutronix.de>,
rostedt <rostedt@goodmis.org>,
David Howells <dhowells@redhat.com>,
Eric Dumazet <edumazet@google.com>, fweisbec <fweisbec@gmail.com>,
Oleg Nesterov <oleg@redhat.com>,
Boqun Feng <boqun.feng@gmail.com>, Andrew Hunter <ahh@google.com>,
maged michael <maged.michael@gmail.com>,
gromer <gromer@google.com>, Avi Kivity <avi@scylladb.com>,
Benjamin Herrenschmidt <benh@kernel.crashing.org>,
Paul Mackerras <paulus@samba.org>,
Michael Ellerman <mpe@ellerman.id.au>,
Dave Watson <davejwatson@fb.com>,
Alan Stern <stern@rowland.harvard.edu>,
Will Deacon <will.deacon@arm.com>,
Andy Lutomirski <luto@kernel.org>, Ingo Molnar <mingo@redhat.com>,
Alexander Viro <viro@zeniv.linux.org.uk>,
Nicholas Piggin <npiggin@gmail.com>,
linuxppc-dev <linuxppc-dev@lists.ozlabs.org>,
linux-arch <linux-arch@vger.kernel.org>
Subject: Re: [PATCH tip/core/rcu 1/3] membarrier: Provide register expedited private command
Date: Sat, 7 Oct 2017 17:10:04 +0200 [thread overview]
Message-ID: <20171007151004.GA3874@andrea> (raw)
Message-ID: <20171007151004.zN7KK_LorwPQo4DIiP2nQgmaJ-XJRo7xasy9oSeVa_o@z> (raw)
In-Reply-To: <20171006083219.asdpl5w4pl6hedcd@hirez.programming.kicks-ass.net>
On Fri, Oct 06, 2017 at 10:32:19AM +0200, Peter Zijlstra wrote:
> > AFAIU the scheduler rq->lock is held while preemption is disabled.
> > synchronize_sched() is used here to ensure that all pre-existing
> > preempt-off critical sections have completed.
> >
> > So saying that we use synchronize_sched() to synchronize with rq->lock
> > would be stretching the truth a bit. It's actually only true because the
> > scheduler holding the rq->lock is surrounded by a preempt-off
> > critical section.
>
> No, rq->lock is sufficient, note that rq->lock is a raw_spinlock_t which
> implies !preempt. Yes, we also surround the rq->lock usage with a
> slightly larger preempt_disable() section but that's not in fact
> required for this.
That's what it is, according to the current sources: we seemed to agree that
a preempt-off critical section is what we rely on here and that the start of
this critical section is not marked by that raw_spin_lock.
Andrea
next prev parent reply other threads:[~2017-10-07 15:10 UTC|newest]
Thread overview: 37+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-10-04 21:37 [PATCH tip/core/rcu 0/3] Updates to sys_membarrier for v4.14 to add registration Paul E. McKenney
2017-10-04 21:37 ` [PATCH tip/core/rcu 1/3] membarrier: Provide register expedited private command Paul E. McKenney
2017-10-04 21:37 ` Paul E. McKenney
2017-10-05 4:23 ` Nicholas Piggin
2017-10-05 4:23 ` Nicholas Piggin
2017-10-05 12:22 ` Avi Kivity
2017-10-05 12:22 ` Avi Kivity
2017-10-05 15:54 ` Mathieu Desnoyers
2017-10-05 15:54 ` Mathieu Desnoyers
2017-10-05 15:53 ` Mathieu Desnoyers
2017-10-05 15:53 ` Mathieu Desnoyers
2017-10-05 12:12 ` Peter Zijlstra
2017-10-05 12:12 ` Peter Zijlstra
2017-10-05 12:24 ` Peter Zijlstra
2017-10-05 12:24 ` Peter Zijlstra
2017-10-05 16:05 ` Mathieu Desnoyers
2017-10-05 16:05 ` Mathieu Desnoyers
2017-10-05 16:02 ` Mathieu Desnoyers
2017-10-05 16:02 ` Mathieu Desnoyers
2017-10-05 16:21 ` Peter Zijlstra
2017-10-05 16:21 ` Peter Zijlstra
2017-10-05 21:44 ` Mathieu Desnoyers
2017-10-05 21:44 ` Mathieu Desnoyers
2017-10-05 22:02 ` Andrea Parri
2017-10-05 22:02 ` Andrea Parri
2017-10-05 22:04 ` Andrea Parri
2017-10-05 22:19 ` Mathieu Desnoyers
2017-10-05 22:19 ` Mathieu Desnoyers
2017-10-05 22:46 ` Steven Rostedt
2017-10-05 22:46 ` Steven Rostedt
2017-10-06 8:32 ` Peter Zijlstra
2017-10-06 8:32 ` Peter Zijlstra
2017-10-07 15:10 ` Andrea Parri [this message]
2017-10-07 15:10 ` Andrea Parri
2017-10-04 21:37 ` [PATCH tip/core/rcu 2/3] membarrier: selftest: Test private expedited cmd Paul E. McKenney
2017-10-04 21:37 ` Paul E. McKenney
2017-10-04 21:37 ` [PATCH tip/core/rcu 3/3] membarrier: Document scheduler barrier requirements 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=20171007151004.GA3874@andrea \
--to=parri.andrea@gmail.com \
--cc=ahh@google.com \
--cc=akpm@linux-foundation.org \
--cc=avi@scylladb.com \
--cc=benh@kernel.crashing.org \
--cc=boqun.feng@gmail.com \
--cc=dhowells@redhat.com \
--cc=dipankar@in.ibm.com \
--cc=edumazet@google.com \
--cc=fweisbec@gmail.com \
--cc=gromer@google.com \
--cc=jiangshanlai@gmail.com \
--cc=josh@joshtriplett.org \
--cc=linux-kernel@vger.kernel.org \
--cc=maged.michael@gmail.com \
--cc=mathieu.desnoyers@efficios.com \
--cc=mingo@kernel.org \
--cc=oleg@redhat.com \
--cc=paulmck@linux.vnet.ibm.com \
--cc=peterz@infradead.org \
--cc=rostedt@goodmis.org \
--cc=tglx@linutronix.de \
/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 an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.