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Message-ID: <CAC4Lta3D5BWnQ5vYjyZTgEvvdSiBK4=i8iaPZN6Ru+jt75hZwQ@mail.gmail.com> Date: Thu, 3 Jan 2013 17:05:44 +0530 From: Raghavendra KT <raghavendra.kt.linux@...il.com> To: Rik van Riel <riel@...hat.com> Cc: linux-kernel@...r.kernel.org, aquini@...hat.com, walken@...gle.com, eric.dumazet@...il.com, lwoodman@...hat.com, jeremy@...p.org, Jan Beulich <JBeulich@...ell.com>, Thomas Gleixner <tglx@...utronix.de>, knoel@...hat.com, Raghavendra KT <raghavendra.kt@...ux.vnet.ibm.com> Subject: Re: [RFC PATCH 2/5] x86,smp: proportional backoff for ticket spinlocks [Ccing IBM id] On Thu, Jan 3, 2013 at 10:52 AM, Rik van Riel <riel@...hat.com> wrote: > Simple fixed value proportional backoff for ticket spinlocks. > By pounding on the cacheline with the spin lock less often, > bus traffic is reduced. In cases of a data structure with > embedded spinlock, the lock holder has a better chance of > making progress. > > If we are next in line behind the current holder of the > lock, we do a fast spin, so as not to waste any time when > the lock is released. > > The number 50 is likely to be wrong for many setups, and > this patch is mostly to illustrate the concept of proportional > backup. The next patch automatically tunes the delay value. > > Signed-off-by: Rik van Riel <riel@...hat.com> > Signed-off-by: Michel Lespinasse <walken@...gle.com> > --- > arch/x86/kernel/smp.c | 23 ++++++++++++++++++++--- > 1 files changed, 20 insertions(+), 3 deletions(-) > > diff --git a/arch/x86/kernel/smp.c b/arch/x86/kernel/smp.c > index 20da354..9c56fe3 100644 > --- a/arch/x86/kernel/smp.c > +++ b/arch/x86/kernel/smp.c > @@ -117,11 +117,28 @@ static bool smp_no_nmi_ipi = false; > */ > void ticket_spin_lock_wait(arch_spinlock_t *lock, struct __raw_tickets inc) > { > + __ticket_t head = inc.head, ticket = inc.tail; > + __ticket_t waiters_ahead; > + unsigned loops; > + > for (;;) { > - cpu_relax(); > - inc.head = ACCESS_ONCE(lock->tickets.head); > + waiters_ahead = ticket - head - 1; ^^^^^^^^^^^^^^ Just wondering, Does wraparound affects this? -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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