* [PATCH RFC srcu] Expedite srcu_schedule_cbs_snp() callback invocation @ 2017-04-18 17:33 Paul E. McKenney 2017-04-18 17:43 ` Marc Zyngier 0 siblings, 1 reply; 3+ messages in thread From: Paul E. McKenney @ 2017-04-18 17:33 UTC (permalink / raw) To: marc.zyngier; +Cc: linux-kernel Although Tree SRCU does reduce delays when there is at least one synchronize_srcu_expedited() invocation pending, srcu_schedule_cbs_snp() still waits for SRCU_INTERVAL before invoking callbacks. Since synchronize_srcu_expedited() now posts a callback and waits for that callback to do a wakeup, this destroys the expedited nature of synchronize_srcu_expedited(). This commit therefore invokes callbacks immediately at the end of the grace period when there is at least one synchronize_srcu_expedited() invocation pending. Reported-by: Marc Zyngier <marc.zyngier@arm.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c index 1e54f91c2ff7..744ffdb79d23 100644 --- a/kernel/rcu/srcutree.c +++ b/kernel/rcu/srcutree.c @@ -447,7 +447,8 @@ static void srcu_schedule_cbs_snp(struct srcu_struct *sp, struct srcu_node *snp) int cpu; for (cpu = snp->grplo; cpu <= snp->grphi; cpu++) - srcu_schedule_cbs_sdp(per_cpu_ptr(sp->sda, cpu), SRCU_INTERVAL); + srcu_schedule_cbs_sdp(per_cpu_ptr(sp->sda, cpu), + atomic_read(&sp->srcu_exp_cnt) ? 0 : SRCU_INTERVAL); } /* ^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH RFC srcu] Expedite srcu_schedule_cbs_snp() callback invocation 2017-04-18 17:33 [PATCH RFC srcu] Expedite srcu_schedule_cbs_snp() callback invocation Paul E. McKenney @ 2017-04-18 17:43 ` Marc Zyngier 2017-04-18 17:50 ` Paul E. McKenney 0 siblings, 1 reply; 3+ messages in thread From: Marc Zyngier @ 2017-04-18 17:43 UTC (permalink / raw) To: paulmck; +Cc: linux-kernel On 18/04/17 18:33, Paul E. McKenney wrote: > Although Tree SRCU does reduce delays when there is at least one > synchronize_srcu_expedited() invocation pending, srcu_schedule_cbs_snp() > still waits for SRCU_INTERVAL before invoking callbacks. Since > synchronize_srcu_expedited() now posts a callback and waits for > that callback to do a wakeup, this destroys the expedited nature of > synchronize_srcu_expedited(). > > This commit therefore invokes callbacks immediately at the end of the > grace period when there is at least one synchronize_srcu_expedited() > invocation pending. > > Reported-by: Marc Zyngier <marc.zyngier@arm.com> > Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> > > diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c > index 1e54f91c2ff7..744ffdb79d23 100644 > --- a/kernel/rcu/srcutree.c > +++ b/kernel/rcu/srcutree.c > @@ -447,7 +447,8 @@ static void srcu_schedule_cbs_snp(struct srcu_struct *sp, struct srcu_node *snp) > int cpu; > > for (cpu = snp->grplo; cpu <= snp->grphi; cpu++) > - srcu_schedule_cbs_sdp(per_cpu_ptr(sp->sda, cpu), SRCU_INTERVAL); > + srcu_schedule_cbs_sdp(per_cpu_ptr(sp->sda, cpu), > + atomic_read(&sp->srcu_exp_cnt) ? 0 : SRCU_INTERVAL); > } > > /* This fixes the issue I was observing, where UEFI in a KVM guest would take a x8 slowdown while it messes with some NOR flash emulation on arm64 (don't ask, this is horrible...). Anyway: Tested-by: Marc Zyngier <marc.zyngier@arm.com> Thanks again Paul! M. -- Jazz is not dead. It just smells funny... ^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH RFC srcu] Expedite srcu_schedule_cbs_snp() callback invocation 2017-04-18 17:43 ` Marc Zyngier @ 2017-04-18 17:50 ` Paul E. McKenney 0 siblings, 0 replies; 3+ messages in thread From: Paul E. McKenney @ 2017-04-18 17:50 UTC (permalink / raw) To: Marc Zyngier; +Cc: linux-kernel On Tue, Apr 18, 2017 at 06:43:05PM +0100, Marc Zyngier wrote: > On 18/04/17 18:33, Paul E. McKenney wrote: > > Although Tree SRCU does reduce delays when there is at least one > > synchronize_srcu_expedited() invocation pending, srcu_schedule_cbs_snp() > > still waits for SRCU_INTERVAL before invoking callbacks. Since > > synchronize_srcu_expedited() now posts a callback and waits for > > that callback to do a wakeup, this destroys the expedited nature of > > synchronize_srcu_expedited(). > > > > This commit therefore invokes callbacks immediately at the end of the > > grace period when there is at least one synchronize_srcu_expedited() > > invocation pending. > > > > Reported-by: Marc Zyngier <marc.zyngier@arm.com> > > Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> > > > > diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c > > index 1e54f91c2ff7..744ffdb79d23 100644 > > --- a/kernel/rcu/srcutree.c > > +++ b/kernel/rcu/srcutree.c > > @@ -447,7 +447,8 @@ static void srcu_schedule_cbs_snp(struct srcu_struct *sp, struct srcu_node *snp) > > int cpu; > > > > for (cpu = snp->grplo; cpu <= snp->grphi; cpu++) > > - srcu_schedule_cbs_sdp(per_cpu_ptr(sp->sda, cpu), SRCU_INTERVAL); > > + srcu_schedule_cbs_sdp(per_cpu_ptr(sp->sda, cpu), > > + atomic_read(&sp->srcu_exp_cnt) ? 0 : SRCU_INTERVAL); > > } > > > > /* > > This fixes the issue I was observing, where UEFI in a KVM guest would > take a x8 slowdown while it messes with some NOR flash emulation on > arm64 (don't ask, this is horrible...). Anyway: > > Tested-by: Marc Zyngier <marc.zyngier@arm.com> > > Thanks again Paul! Thank you for your bug-finding and testing efforts! I will be pushing this into the upcoming merge window. Thanx, Paul ------------------------------------------------------------------------ commit 6eec94fe40e294b04d32c8ef552e28fa6159bdad Author: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Date: Tue Apr 18 10:28:31 2017 -0700 srcu: Expedite srcu_schedule_cbs_snp() callback invocation Although Tree SRCU does reduce delays when there is at least one synchronize_srcu_expedited() invocation pending, srcu_schedule_cbs_snp() still waits for SRCU_INTERVAL before invoking callbacks. Since synchronize_srcu_expedited() now posts a callback and waits for that callback to do a wakeup, this destroys the expedited nature of synchronize_srcu_expedited(). This destruction became apparent to Marc Zyngier in the guise of a guest-OS bootup slowdown from five seconds to no fewer than forty seconds. This commit therefore invokes callbacks immediately at the end of the grace period when there is at least one synchronize_srcu_expedited() invocation pending. This brought Marc's guest-OS bootup times back into the realm of reason. Reported-by: Marc Zyngier <marc.zyngier@arm.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Tested-by: Marc Zyngier <marc.zyngier@arm.com> diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c index 1e54f91c2ff7..744ffdb79d23 100644 --- a/kernel/rcu/srcutree.c +++ b/kernel/rcu/srcutree.c @@ -447,7 +447,8 @@ static void srcu_schedule_cbs_snp(struct srcu_struct *sp, struct srcu_node *snp) int cpu; for (cpu = snp->grplo; cpu <= snp->grphi; cpu++) - srcu_schedule_cbs_sdp(per_cpu_ptr(sp->sda, cpu), SRCU_INTERVAL); + srcu_schedule_cbs_sdp(per_cpu_ptr(sp->sda, cpu), + atomic_read(&sp->srcu_exp_cnt) ? 0 : SRCU_INTERVAL); } /* ^ permalink raw reply related [flat|nested] 3+ messages in thread
end of thread, other threads:[~2017-04-18 17:50 UTC | newest] Thread overview: 3+ messages (download: mbox.gz follow: Atom feed -- links below jump to the message on this page -- 2017-04-18 17:33 [PATCH RFC srcu] Expedite srcu_schedule_cbs_snp() callback invocation Paul E. McKenney 2017-04-18 17:43 ` Marc Zyngier 2017-04-18 17:50 ` Paul E. McKenney
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