Messages in this thread Patch in this message | | | From | "Paul E. McKenney" <> | Subject | [PATCH v3 tip/core/rcu 39/40] srcu: Expedite srcu_schedule_cbs_snp() callback invocation | Date | Wed, 19 Apr 2017 09:58:36 -0700 |
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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> --- kernel/rcu/srcutree.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c index f9c684d79faa..e11b89a363f7 100644 --- a/kernel/rcu/srcutree.c +++ b/kernel/rcu/srcutree.c @@ -442,7 +442,8 @@ 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); } /* -- 2.5.2
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