All the mail mirrored from lore.kernel.org
 help / color / mirror / Atom feed
From: Peter Zijlstra <peterz@infradead.org>
To: Waiman Long <waiman.long@hpe.com>
Cc: Ingo Molnar <mingo@redhat.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	"H. Peter Anvin" <hpa@zytor.com>,
	x86@kernel.org, linux-kernel@vger.kernel.org,
	Scott J Norton <scott.norton@hp.com>,
	Douglas Hatch <doug.hatch@hp.com>,
	Davidlohr Bueso <dave@stgolabs.net>
Subject: Re: [PATCH v6 5/6] locking/pvqspinlock: Allow 1 lock stealing attempt
Date: Wed, 16 Sep 2015 17:01:31 +0200	[thread overview]
Message-ID: <20150916150131.GC3604@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <55F8394A.1010809@hpe.com>

On Tue, Sep 15, 2015 at 11:29:14AM -0400, Waiman Long wrote:

> Only the queue head vCPU will be in pv_wait_head() spinning to acquire the
> lock.

But what will guarantee fwd progress for the lock that is the head?

Suppose CPU0 becomes head and enters the /* claim the lock */ loop.

Then CPU1 comes in, steals it in pv_wait_head(). CPU1 releases, CPU1
re-acquires and _again_ steals in pv_wait_head(), etc..

All the while CPU0 doesn't go anywhere.


  reply	other threads:[~2015-09-16 15:07 UTC|newest]

Thread overview: 32+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-09-11 18:37 [PATCH v6 0/6] locking/qspinlock: Enhance pvqspinlock performance Waiman Long
2015-09-11 18:37 ` [PATCH v6 1/6] locking/qspinlock: relaxes cmpxchg & xchg ops in native code Waiman Long
2015-09-11 22:27   ` Davidlohr Bueso
2015-09-14 12:06     ` Peter Zijlstra
2015-09-14 18:40       ` Waiman Long
2015-09-14 15:16     ` Waiman Long
2015-09-11 18:37 ` [PATCH v6 2/6] locking/pvqspinlock: Unconditional PV kick with _Q_SLOW_VAL Waiman Long
2015-09-18  8:50   ` [tip:locking/core] locking/pvqspinlock: Kick the PV CPU unconditionally when _Q_SLOW_VAL tip-bot for Waiman Long
2015-09-11 18:37 ` [PATCH v6 3/6] locking/pvqspinlock, x86: Optimize PV unlock code path Waiman Long
2015-09-11 18:37 ` [PATCH v6 4/6] locking/pvqspinlock: Collect slowpath lock statistics Waiman Long
2015-09-11 23:13   ` Davidlohr Bueso
2015-09-14 15:25     ` Waiman Long
2015-09-14 21:41       ` Davidlohr Bueso
2015-09-15  3:47         ` Waiman Long
2015-09-11 18:37 ` [PATCH v6 5/6] locking/pvqspinlock: Allow 1 lock stealing attempt Waiman Long
2015-09-14 13:57   ` Peter Zijlstra
2015-09-14 19:02     ` Waiman Long
2015-09-14 14:00   ` Peter Zijlstra
2015-09-14 19:15     ` Waiman Long
2015-09-14 19:38       ` Waiman Long
2015-09-15  8:24       ` Peter Zijlstra
2015-09-15 15:29         ` Waiman Long
2015-09-16 15:01           ` Peter Zijlstra [this message]
2015-09-17 15:08             ` Waiman Long
2015-09-14 14:04   ` Peter Zijlstra
2015-09-14 19:19     ` Waiman Long
2015-09-11 18:37 ` [PATCH v6 6/6] locking/pvqspinlock: Queue node adaptive spinning Waiman Long
2015-09-14 14:10   ` Peter Zijlstra
2015-09-14 19:37     ` Waiman Long
2015-09-15  8:38       ` Peter Zijlstra
2015-09-15 15:32         ` Waiman Long
2015-09-16 15:03           ` Peter Zijlstra

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=20150916150131.GC3604@twins.programming.kicks-ass.net \
    --to=peterz@infradead.org \
    --cc=dave@stgolabs.net \
    --cc=doug.hatch@hp.com \
    --cc=hpa@zytor.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=mingo@redhat.com \
    --cc=scott.norton@hp.com \
    --cc=tglx@linutronix.de \
    --cc=waiman.long@hpe.com \
    --cc=x86@kernel.org \
    /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.