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From: Peter Zijlstra <peterz@infradead.org>
To: Waiman Long <waiman.long@hp.com>
Cc: tglx@linutronix.de, mingo@redhat.com, hpa@zytor.com,
	paolo.bonzini@gmail.com, konrad.wilk@oracle.com,
	boris.ostrovsky@oracle.com, paulmck@linux.vnet.ibm.com,
	riel@redhat.com, torvalds@linux-foundation.org,
	raghavendra.kt@linux.vnet.ibm.com, david.vrabel@citrix.com,
	oleg@redhat.com, scott.norton@hp.com, doug.hatch@hp.com,
	linux-arch@vger.kernel.org, x86@kernel.org,
	linux-kernel@vger.kernel.org,
	virtualization@lists.linux-foundation.org,
	xen-devel@lists.xenproject.org, kvm@vger.kernel.org,
	luto@amacapital.net
Subject: Re: [PATCH 8/9] qspinlock: Generic paravirt support
Date: Thu, 19 Mar 2015 14:43:36 +0100	[thread overview]
Message-ID: <20150319134336.GE11574@worktop.ger.corp.intel.com> (raw)
In-Reply-To: <20150319122536.GD11574@worktop.ger.corp.intel.com>

On Thu, Mar 19, 2015 at 01:25:36PM +0100, Peter Zijlstra wrote:
> +static struct qspinlock **pv_hash(struct qspinlock *lock)
> +{
> +	u32 hash = hash_ptr(lock, PV_LOCK_HASH_BITS);
> +	struct pv_hash_bucket *hb, *end;
> +
> +	if (!hash)
> +		hash = 1;
> +
> +	hb = &__pv_lock_hash[hash_align(hash)];
> +	for (;;) {
> +		for (end = hb + PV_HB_PER_LINE; hb < end; hb++) {
> +			if (cmpxchg(&hb->lock, NULL, HB_RESERVED)) {

That should be: !cmpxchg(), bit disturbing that that booted.

> +				WRITE_ONCE(hb->cpu, smp_processor_id());
> +				/*
> +				 * Since we must read lock first and cpu
> +				 * second, we must write cpu first and lock
> +				 * second, therefore use HB_RESERVE to mark an
> +				 * entry in use before writing the values.
> +				 *
> +				 * This can cause hb_hash_find() to not find a
> +				 * cpu even though _Q_SLOW_VAL, this is not a
> +				 * problem since we re-check l->locked before
> +				 * going to sleep and the unlock will have
> +				 * cleared l->locked already.
> +				 */
> +				smp_wmb(); /* matches rmb from pv_hash_find */
> +				WRITE_ONCE(hb->lock, lock);
> +				goto done;
> +			}
> +		}
> +
> +		hash = lfsr(hash, PV_LOCK_HASH_BITS);
> +		hb = &__pv_lock_hash[hash_align(hash)];
> +	}
> +
> +done:
> +	return &hb->lock;
> +}

  reply	other threads:[~2015-03-19 13:43 UTC|newest]

Thread overview: 43+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-03-16 13:16 [PATCH 0/9] qspinlock stuff -v15 Peter Zijlstra
2015-03-16 13:16 ` [PATCH 1/9] qspinlock: A simple generic 4-byte queue spinlock Peter Zijlstra
2015-03-16 13:16 ` [PATCH 2/9] qspinlock, x86: Enable x86-64 to use " Peter Zijlstra
2015-03-16 13:16 ` [PATCH 3/9] qspinlock: Add pending bit Peter Zijlstra
2015-03-16 13:16 ` [PATCH 4/9] qspinlock: Extract out code snippets for the next patch Peter Zijlstra
2015-03-16 13:16 ` [PATCH 5/9] qspinlock: Optimize for smaller NR_CPUS Peter Zijlstra
2015-03-16 13:16 ` [PATCH 6/9] qspinlock: Use a simple write to grab the lock Peter Zijlstra
2015-03-16 13:16 ` [PATCH 7/9] qspinlock: Revert to test-and-set on hypervisors Peter Zijlstra
2015-03-16 13:16 ` [PATCH 8/9] qspinlock: Generic paravirt support Peter Zijlstra
     [not found]   ` <5509E51D.7040909@hp.com>
2015-03-19 10:12     ` Peter Zijlstra
2015-03-19 12:25       ` Peter Zijlstra
2015-03-19 13:43         ` Peter Zijlstra [this message]
2015-03-19 23:25         ` Waiman Long
2015-04-01 16:20         ` Waiman Long
2015-04-01 17:12           ` Peter Zijlstra
2015-04-01 17:42             ` Peter Zijlstra
2015-04-01 18:17               ` Peter Zijlstra
2015-04-01 18:54                 ` Waiman Long
2015-04-01 18:48                   ` Peter Zijlstra
2015-04-01 19:58                     ` Waiman Long
2015-04-01 21:03                       ` Peter Zijlstra
2015-04-02 16:28                         ` Waiman Long
2015-04-02 17:20                           ` Peter Zijlstra
2015-04-02 19:48                             ` Peter Zijlstra
2015-04-03  3:39                               ` Waiman Long
2015-04-03 13:43                               ` Peter Zijlstra
2015-04-01 20:10             ` Waiman Long
2015-03-16 13:16 ` [PATCH 9/9] qspinlock,x86,kvm: Implement KVM support for paravirt qspinlock Peter Zijlstra
     [not found]   ` <550A3863.2060808@hp.com>
2015-03-19 10:01     ` Peter Zijlstra
2015-03-19 21:08       ` Waiman Long
2015-03-20  7:43         ` Raghavendra K T
2015-03-16 14:08 ` [Xen-devel] [PATCH 0/9] qspinlock stuff -v15 David Vrabel
2015-03-18 20:36 ` Waiman Long
2015-03-19 18:01 ` [Xen-devel] " David Vrabel
2015-03-19 18:32   ` Peter Zijlstra
2015-03-25 19:47 ` Konrad Rzeszutek Wilk
2015-03-26 20:21   ` Peter Zijlstra
2015-03-27 14:07     ` Konrad Rzeszutek Wilk
2015-03-30 16:41       ` Waiman Long
2015-03-30 16:25   ` Waiman Long
2015-03-30 16:29     ` Peter Zijlstra
2015-03-30 16:43       ` Waiman Long
2015-03-27  6:40 ` Raghavendra K T

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