From: "Nicholas Piggin" <npiggin@gmail•com>
To: "Jordan Niethe" <jniethe5@gmail•com>, <linuxppc-dev@lists•ozlabs.org>
Subject: Re: [PATCH 09/17] powerpc/qspinlock: implement option to yield to previous node
Date: Thu, 10 Nov 2022 21:14:26 +1000 [thread overview]
Message-ID: <CO8KLWDWSQDW.273LILF6ZT13O@bobo> (raw)
In-Reply-To: <c56326f5d55db6b8f6a611ae130e0e5362b39ceb.camel@gmail.com>
On Thu Nov 10, 2022 at 10:41 AM AEST, Jordan Niethe wrote:
> On Thu, 2022-07-28 at 16:31 +1000, Nicholas Piggin wrote:
> [resend as utf-8, not utf-7]
> > Queued waiters which are not at the head of the queue don't spin on
> > the lock word but their qnode lock word, waiting for the previous queued
> > CPU to release them. Add an option which allows these waiters to yield
> > to the previous CPU if its vCPU is preempted.
> >
> > Disable this option by default for now, i.e., no logical change.
> > ---
> > arch/powerpc/lib/qspinlock.c | 46 +++++++++++++++++++++++++++++++++++-
> > 1 file changed, 45 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/powerpc/lib/qspinlock.c b/arch/powerpc/lib/qspinlock.c
> > index 55286ac91da5..b39f8c5b329c 100644
> > --- a/arch/powerpc/lib/qspinlock.c
> > +++ b/arch/powerpc/lib/qspinlock.c
> > @@ -26,6 +26,7 @@ static bool MAYBE_STEALERS __read_mostly = true;
> > static int HEAD_SPINS __read_mostly = (1<<8);
> >
> > static bool pv_yield_owner __read_mostly = true;
> > +static bool pv_yield_prev __read_mostly = true;
>
> Similiar suggestion, maybe pv_yield_prev_enabled would read better.
>
> Isn't this enabled by default contrary to the commit message?
Yeah a few of those changelogs got out of synch.
>
> >
> > static DEFINE_PER_CPU_ALIGNED(struct qnodes, qnodes);
> >
> > @@ -224,6 +225,31 @@ static __always_inline void yield_to_locked_owner(struct qspinlock *lock, u32 va
> > cpu_relax();
> > }
> >
> > +static __always_inline void yield_to_prev(struct qspinlock *lock, struct qnode *node, int prev_cpu, bool paravirt)
>
> yield_to_locked_owner() takes a raw val and works out the cpu to yield to.
> I think for consistency have yield_to_prev() take the raw val and work it out too.
Good thinking.
> > +{
> > + u32 yield_count;
> > +
> > + if (!paravirt)
> > + goto relax;
> > +
> > + if (!pv_yield_prev)
> > + goto relax;
> > +
> > + yield_count = yield_count_of(prev_cpu);
> > + if ((yield_count & 1) == 0)
> > + goto relax; /* owner vcpu is running */
> > +
> > + smp_rmb(); /* See yield_to_locked_owner comment */
> > +
> > + if (!node->locked) {
> > + yield_to_preempted(prev_cpu, yield_count);
> > + return;
> > + }
> > +
> > +relax:
> > + cpu_relax();
> > +}
> > +
> >
> > static __always_inline bool try_to_steal_lock(struct qspinlock *lock, bool paravirt)
> > {
> > @@ -291,13 +317,14 @@ static __always_inline void queued_spin_lock_mcs_queue(struct qspinlock *lock, b
> > */
> > if (old & _Q_TAIL_CPU_MASK) {
> > struct qnode *prev = get_tail_qnode(lock, old);
> > + int prev_cpu = get_tail_cpu(old);
>
> This could then be removed.
>
> >
> > /* Link @node into the waitqueue. */
> > WRITE_ONCE(prev->next, node);
> >
> > /* Wait for mcs node lock to be released */
> > while (!node->locked)
> > - cpu_relax();
> > + yield_to_prev(lock, node, prev_cpu, paravirt);
>
> And would have this as:
> yield_to_prev(lock, node, old, paravirt);
Yep.
Thanks,
Nick
next prev parent reply other threads:[~2022-11-10 11:15 UTC|newest]
Thread overview: 78+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-07-28 6:31 [PATCH 00/17] powerpc: alternate queued spinlock implementation Nicholas Piggin
2022-07-28 6:31 ` [PATCH 01/17] powerpc/qspinlock: powerpc qspinlock implementation Nicholas Piggin
2022-08-10 1:52 ` Jordan NIethe
2022-08-10 6:48 ` Christophe Leroy
2022-11-10 0:35 ` Jordan Niethe
2022-11-10 6:37 ` Christophe Leroy
2022-11-10 11:44 ` Nicholas Piggin
2022-11-10 9:09 ` Nicholas Piggin
2022-07-28 6:31 ` [PATCH 1a/17] powerpc/qspinlock: Prepare qspinlock code Nicholas Piggin
2022-07-28 6:31 ` [PATCH 02/17] powerpc/qspinlock: add mcs queueing for contended waiters Nicholas Piggin
2022-08-10 2:28 ` Jordan NIethe
2022-11-10 0:36 ` Jordan Niethe
2022-11-10 9:21 ` Nicholas Piggin
2022-07-28 6:31 ` [PATCH 03/17] powerpc/qspinlock: use a half-word store to unlock to avoid larx/stcx Nicholas Piggin
2022-08-10 3:28 ` Jordan Niethe
2022-11-10 0:39 ` Jordan Niethe
2022-11-10 9:25 ` Nicholas Piggin
2022-07-28 6:31 ` [PATCH 04/17] powerpc/qspinlock: convert atomic operations to assembly Nicholas Piggin
2022-08-10 3:54 ` Jordan Niethe
2022-11-10 0:39 ` Jordan Niethe
2022-11-10 8:36 ` Christophe Leroy
2022-11-10 11:48 ` Nicholas Piggin
2022-11-10 9:40 ` Nicholas Piggin
2022-07-28 6:31 ` [PATCH 05/17] powerpc/qspinlock: allow new waiters to steal the lock before queueing Nicholas Piggin
2022-08-10 4:31 ` Jordan Niethe
2022-11-10 0:40 ` Jordan Niethe
2022-11-10 10:54 ` Nicholas Piggin
2022-07-28 6:31 ` [PATCH 06/17] powerpc/qspinlock: theft prevention to control latency Nicholas Piggin
2022-08-10 5:51 ` Jordan Niethe
2022-11-10 0:40 ` Jordan Niethe
2022-11-10 10:57 ` Nicholas Piggin
2022-07-28 6:31 ` [PATCH 07/17] powerpc/qspinlock: store owner CPU in lock word Nicholas Piggin
2022-08-12 0:50 ` Jordan Niethe
2022-11-10 0:40 ` Jordan Niethe
2022-11-10 10:59 ` Nicholas Piggin
2022-07-28 6:31 ` [PATCH 08/17] powerpc/qspinlock: paravirt yield to lock owner Nicholas Piggin
2022-08-12 2:01 ` Jordan Niethe
2022-11-10 0:41 ` Jordan Niethe
2022-11-10 11:13 ` Nicholas Piggin
2022-07-28 6:31 ` [PATCH 09/17] powerpc/qspinlock: implement option to yield to previous node Nicholas Piggin
2022-08-12 2:07 ` Jordan Niethe
2022-11-10 0:41 ` Jordan Niethe
2022-11-10 11:14 ` Nicholas Piggin [this message]
2022-07-28 6:31 ` [PATCH 10/17] powerpc/qspinlock: allow stealing when head of queue yields Nicholas Piggin
2022-08-12 4:06 ` Jordan Niethe
2022-11-10 0:42 ` Jordan Niethe
2022-11-10 11:22 ` Nicholas Piggin
2022-07-28 6:31 ` [PATCH 11/17] powerpc/qspinlock: allow propagation of yield CPU down the queue Nicholas Piggin
2022-08-12 4:17 ` Jordan Niethe
2022-10-06 17:27 ` Laurent Dufour
2022-11-10 0:42 ` Jordan Niethe
2022-11-10 11:25 ` Nicholas Piggin
2022-07-28 6:31 ` [PATCH 12/17] powerpc/qspinlock: add ability to prod new queue head CPU Nicholas Piggin
2022-08-12 4:22 ` Jordan Niethe
2022-11-10 0:42 ` Jordan Niethe
2022-11-10 11:32 ` Nicholas Piggin
2022-07-28 6:31 ` [PATCH 13/17] powerpc/qspinlock: trylock and initial lock attempt may steal Nicholas Piggin
2022-08-12 4:32 ` Jordan Niethe
2022-11-10 0:43 ` Jordan Niethe
2022-11-10 11:35 ` Nicholas Piggin
2022-07-28 6:31 ` [PATCH 14/17] powerpc/qspinlock: use spin_begin/end API Nicholas Piggin
2022-08-12 4:36 ` Jordan Niethe
2022-11-10 0:43 ` Jordan Niethe
2022-11-10 11:36 ` Nicholas Piggin
2022-07-28 6:31 ` [PATCH 15/17] powerpc/qspinlock: reduce remote node steal spins Nicholas Piggin
2022-08-12 4:43 ` Jordan Niethe
2022-11-10 0:43 ` Jordan Niethe
2022-11-10 11:37 ` Nicholas Piggin
2022-07-28 6:31 ` [PATCH 16/17] powerpc/qspinlock: allow indefinite spinning on a preempted owner Nicholas Piggin
2022-08-12 4:49 ` Jordan Niethe
2022-09-22 15:02 ` Laurent Dufour
2022-09-23 8:16 ` Nicholas Piggin
2022-11-10 0:44 ` Jordan Niethe
2022-11-10 11:38 ` Nicholas Piggin
2022-07-28 6:31 ` [PATCH 17/17] powerpc/qspinlock: provide accounting and options for sleepy locks Nicholas Piggin
2022-08-15 1:11 ` Jordan Niethe
2022-11-10 0:44 ` Jordan Niethe
2022-11-10 11:41 ` Nicholas Piggin
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=CO8KLWDWSQDW.273LILF6ZT13O@bobo \
--to=npiggin@gmail$(echo .)com \
--cc=jniethe5@gmail$(echo .)com \
--cc=linuxppc-dev@lists$(echo .)ozlabs.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox