From: Peter Zijlstra <peterz@infradead.org>
To: Alex Kogan <alex.kogan@oracle.com>
Cc: linux-arch@vger.kernel.org, guohanjun@huawei.com, arnd@arndb.de,
dave.dice@oracle.com, jglauber@marvell.com, x86@kernel.org,
will.deacon@arm.com, linux@armlinux.org.uk,
steven.sistare@oracle.com, linux-kernel@vger.kernel.org,
rahul.x.yadav@oracle.com, mingo@redhat.com, bp@alien8.de,
hpa@zytor.com, longman@redhat.com, tglx@linutronix.de,
daniel.m.jordan@oracle.com, linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v3 3/5] locking/qspinlock: Introduce CNA into the slow path of qspinlock
Date: Wed, 17 Jul 2019 10:39:44 +0200 [thread overview]
Message-ID: <20190717083944.GR3463@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20190716184724.GH3402@hirez.programming.kicks-ass.net>
On Tue, Jul 16, 2019 at 08:47:24PM +0200, Peter Zijlstra wrote:
> On Tue, Jul 16, 2019 at 01:19:16PM -0400, Alex Kogan wrote:
> > > On Jul 16, 2019, at 11:50 AM, Peter Zijlstra <peterz@infradead.org> wrote:
>
> > > static void cna_move(struct cna_node *cn, struct cna_node *cni)
> > > {
> > > struct cna_node *head, *tail;
> > >
> > > /* remove @cni */
> > > WRITE_ONCE(cn->mcs.next, cni->mcs.next);
> > >
> > > /* stick @cni on the 'other' list tail */
> > > cni->mcs.next = NULL;
> > >
> > > if (cn->mcs.locked <= 1) {
> > > /* head = tail = cni */
> > > head = cni;
> > > head->tail = cni;
> > > cn->mcs.locked = head->encoded_tail;
> > > } else {
> > > /* add to tail */
> > > head = (struct cna_node *)decode_tail(cn->mcs.locked);
> > > tail = tail->tail;
> > > tail->next = cni;
> > > }
> > > }
> > >
> > > static struct cna_node *cna_find_next(struct mcs_spinlock *node)
> > > {
> > > struct cna_node *cni, *cn = (struct cna_node *)node;
> > >
> > > while ((cni = (struct cna_node *)READ_ONCE(cn->mcs.next))) {
> > > if (likely(cni->node == cn->node))
> > > break;
> > >
> > > cna_move(cn, cni);
> > > }
> > >
> > > return cni;
> > > }
> > But then you move nodes from the main list to the ‘other’ list one-by-one.
> > I’m afraid this would be unnecessary expensive.
> > Plus, all this extra work is wasted if you do not find a thread on the same
> > NUMA node (you move everyone to the ‘other’ list only to move them back in
> > cna_mcs_pass_lock()).
>
> My primary concern was readability; I find the above suggestion much
> more readable. Maybe it can be written differently; you'll have to play
> around a bit.
static void cna_splice_tail(struct cna_node *cn, struct cna_node *head, struct cna_node *tail)
{
struct cna_node *list;
/* remove [head,tail] */
WRITE_ONCE(cn->mcs.next, tail->mcs.next);
tail->mcs.next = NULL;
/* stick [head,tail] on the secondary list tail */
if (cn->mcs.locked <= 1) {
/* create secondary list */
head->tail = tail;
cn->mcs.locked = head->encoded_tail;
} else {
/* add to tail */
list = (struct cna_node *)decode_tail(cn->mcs.locked);
list->tail->next = head;
list->tail = tail;
}
}
static struct cna_node *cna_find_next(struct mcs_spinlock *node)
{
struct cna_node *cni, *cn = (struct cna_node *)node;
struct cna_node *head, *tail = NULL;
/* find any next lock from 'our' node */
for (head = cni = (struct cna_node *)READ_ONCE(cn->mcs.next);
cni && cni->node != cn->node;
tail = cni, cni = (struct cna_node *)READ_ONCE(cni->mcs.next))
;
/* when found, splice any skipped locks onto the secondary list */
if (cni && tail)
cna_splice_tail(cn, head, tail);
return cni;
}
How's that?
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next prev parent reply other threads:[~2019-07-17 8:39 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-15 19:25 [PATCH v3 0/5] Add NUMA-awareness to qspinlock Alex Kogan
2019-07-15 19:25 ` [PATCH v3 1/5] locking/qspinlock: Make arch_mcs_spin_unlock_contended more generic Alex Kogan
2019-07-16 10:23 ` Peter Zijlstra
2019-07-15 19:25 ` [PATCH v3 2/5] locking/qspinlock: Refactor the qspinlock slow path Alex Kogan
2019-07-16 10:20 ` Peter Zijlstra
2019-07-16 14:53 ` Alex Kogan
2019-07-16 15:58 ` Peter Zijlstra
2019-07-15 19:25 ` [PATCH v3 3/5] locking/qspinlock: Introduce CNA into the slow path of qspinlock Alex Kogan
2019-07-15 21:30 ` Waiman Long
2019-07-16 11:04 ` Peter Zijlstra
2019-07-16 14:26 ` Alex Kogan
2019-07-16 14:44 ` Waiman Long
[not found] ` <aa73b86d-902a-bb6f-d372-8645c8299a6d@redhat.com>
[not found] ` <C1C55A40-FDB1-43B5-B551-F9B8BE776DF8@oracle.com>
2019-07-16 14:50 ` Waiman Long
2019-07-17 17:44 ` Alex Kogan
2019-07-17 17:58 ` Waiman Long
2019-07-16 11:05 ` Peter Zijlstra
2019-07-16 14:30 ` Alex Kogan
2019-07-16 15:50 ` Peter Zijlstra
2019-07-16 17:19 ` Alex Kogan
2019-07-16 18:47 ` Peter Zijlstra
2019-07-17 8:39 ` Peter Zijlstra [this message]
2019-07-17 8:59 ` Peter Zijlstra
2019-07-17 14:52 ` Alex Kogan
[not found] ` <FFC2D45A-24B3-40E1-ABBB-1D696E830B23@oracle.com>
2019-07-17 15:09 ` Peter Zijlstra
2019-07-17 2:16 ` Waiman Long
2019-07-17 7:44 ` Peter Zijlstra
2019-07-17 13:35 ` Waiman Long
2019-07-17 14:42 ` Alex Kogan
2019-07-15 19:25 ` [PATCH v3 4/5] locking/qspinlock: Introduce starvation avoidance into CNA Alex Kogan
2019-07-16 15:59 ` Peter Zijlstra
2019-07-15 19:25 ` [PATCH v3 5/5] locking/qspinlock: Introduce the shuffle reduction optimization " Alex Kogan
2019-07-16 11:47 ` [PATCH v3 0/5] Add NUMA-awareness to qspinlock Nicholas Piggin
[not found] ` <7D29555E-8F72-4EDD-8A87-B1A59C3945A6@oracle.com>
2019-07-16 23:07 ` Nicholas Piggin
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