Path: csiph.com!eternal-september.org!feeder.eternal-september.org!news.mixmin.net!weretis.net!feeder1.news.weretis.net!newsfeed.CARNet.hr!news.spin.it!bofh.it!news.nic.it!robomod From: Peter Zijlstra Newsgroups: linux.kernel Subject: Re: [PATCH v7 4/5] locking/pvqspinlock: Allow 1 lock stealing attempt Date: Tue, 13 Oct 2015 22:00:03 +0200 Message-ID: References: X-Original-To: Waiman Long MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.5.21 (2012-12-30) Sender: robomod@news.nic.it List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Approved: robomod@news.nic.it Lines: 52 Organization: linux.* mail to news gateway X-Original-Cc: Ingo Molnar , Thomas Gleixner , "H. Peter Anvin" , x86@kernel.org, linux-kernel@vger.kernel.org, Scott J Norton , Douglas Hatch , Davidlohr Bueso X-Original-Date: Tue, 13 Oct 2015 21:56:27 +0200 X-Original-Message-ID: <20151013195627.GY3816@twins.programming.kicks-ass.net> X-Original-References: <1442955044-43895-1-git-send-email-Waiman.Long@hpe.com> <1442955044-43895-5-git-send-email-Waiman.Long@hpe.com> X-Original-Sender: linux-kernel-owner@vger.kernel.org Xref: csiph.com linux.kernel:1246098 On Tue, Sep 22, 2015 at 04:50:43PM -0400, Waiman Long wrote: > +gotlock: > /* > + * We now have the lock. We need to either clear the tail code or > + * notify the next one in queue as the new queue head. > */ > + old = atomic_read(&lock->val); > + while ((old & _Q_TAIL_MASK) == tail) { > + int val; > + int new = old & ~_Q_TAIL_MASK; > + > + /* > + * We are the only one in the queue, so clear the tail code > + * and return. > + */ > + val = atomic_cmpxchg(&lock->val, old, new); > + if (old == val) > + goto done; > + old = val; > + } > + This i need to think about a wee bit; its almost the same... So the below is exactly duplicated from the normal slowpath, so why don't you keep that there? It would get you something like: if (pv_wait_head_or_steal(..)) goto stolen; stolen: > + /* > + * contended path; wait for next, release. > + */ > + while (!(next = READ_ONCE(node->next))) > + cpu_relax(); > + > + arch_mcs_spin_unlock_contended(&next->locked); > + pv_kick_node(lock, next); release: ... -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/