Messages in this thread | | | Date | Tue, 12 Jul 2022 10:11:21 +1000 | From | Nicholas Piggin <> | Subject | Re: [PATCH 04/13] locking/qspinlock: move pv lock word helpers into qspinlock.c |
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Excerpts from Waiman Long's message of July 6, 2022 5:34 am: > On 7/4/22 10:38, Nicholas Piggin wrote: >> There is no real reason not to keep all the bit manipulation together. >> >> Signed-off-by: Nicholas Piggin <npiggin@gmail.com> >> --- >> kernel/locking/qspinlock.c | 107 ++++++++++++++++------------ >> kernel/locking/qspinlock_paravirt.h | 51 ------------- >> 2 files changed, 63 insertions(+), 95 deletions(-) >> >> diff --git a/kernel/locking/qspinlock.c b/kernel/locking/qspinlock.c >> index 7360d643de29..8f2173e22479 100644 >> --- a/kernel/locking/qspinlock.c >> +++ b/kernel/locking/qspinlock.c >> @@ -141,7 +141,24 @@ struct qnode *grab_qnode(struct qnode *base, int idx) >> >> #define _Q_LOCKED_PENDING_MASK (_Q_LOCKED_MASK | _Q_PENDING_MASK) >> >> +/** >> + * set_pending - set the pending bit. >> + * @lock: Pointer to queued spinlock structure >> + * >> + * *,0,* -> *,1,* >> + * >> + * The pending bit is used by the queue head vCPU to indicate that it >> + * is actively spinning on the lock and no lock stealing is allowed. > > The pending bit has different usage in pv and non-pv cases. The > description here refers to the pv case. For non-pv, it is used to avoid > loading the the extra node cacheline in likely contended case.
Ah thank you, I can expand on that.
Thanks, Nick
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