On Wed, Jun 08, 2022 at 12:41:28AM +0000, Zhang, Qiang1 wrote:
> On Tue, Jun 07, 2022 at 03:50:57PM +0800, Zqiang wrote:
> > Currently, If the 'rcu_nocb_poll' bootargs is enable, all rcuog
> > kthreads enter polling mode. however, due to only insert CPU's rdp
> > which belong to rcu_nocb_mask to 'nocb_head_rdp' list or all CPU's rdp
> > served by rcuog kthread have been de-offloaded, these cause the
> > 'nocb_head_rdp' list served by rcuog kthread is empty, when the
> > 'nocb_head_rdp' is empty, the rcuog kthread in polling mode not
> > actually do anything. fix it by exiting polling mode when the
> > 'nocb_head_rdp'list is empty, otherwise entering polling mode.
> >
> > Signed-off-by: Zqiang <qiang1.zhang@xxxxxxxxx>
> >
> >This looks a bit more plausible, but what have you done to test this?
>
> Yes , I have only tested as follows and I added two trace events.
>
> + trace_rcu_nocb_wake(rcu_state.name, cpu, TPS("EnterNoPoll"));
> rcu_wait(READ_ONCE(my_rdp->nocb_toggling_rdp));
> + trace_rcu_nocb_wake(rcu_state.name, cpu, TPS("ExitNoPoll"));
>
> runqemu kvm slirp nographic qemuparams="-m 2048 -smp 4" bootparams="rcu_nocbs=2,3 rcutree.dump_tree=1 rcu_nocb_poll rcutorture.nocbs_nthreads=4 rcutorture.test_boost=0" -d
To exercise your change, could you please also add an appropriate value
for the rcutorture.nocbs_nthreads kernel boot parameter? Without that
boot parameter, your kernel will not actually offload or deoffload
any CPUs.
An alternative approach is to run rcutorture scenario TREE01.
Thanx, Paul
> Thanks
> Zqiang
>
> >
> > Thanx, Paul
> >
> > ---
> > v1->v2:
> > Move rcu_nocb_poll flags check from rdp_offload_toggle() to
> > rcu_nocb_rdp_offload/deoffload(), avoid unnecessary setting of
> > rdp_gp->nocb_gp_sleep flags, because when rcu_nocb_poll is set the
> > rdp_gp->nocb_gp_sleep is not used.
> >
> > kernel/rcu/tree_nocb.h | 16 ++++++++++------
> > 1 file changed, 10 insertions(+), 6 deletions(-)
> >
> > diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h index
> > fa8e4f82e60c..2a52c9abc681 100644
> > --- a/kernel/rcu/tree_nocb.h
> > +++ b/kernel/rcu/tree_nocb.h
> > @@ -698,10 +698,14 @@ static void nocb_gp_wait(struct rcu_data *my_rdp)
> > TPS("WakeBypassIsDeferred"));
> > }
> > if (rcu_nocb_poll) {
> > - /* Polling, so trace if first poll in the series. */
> > - if (gotcbs)
> > - trace_rcu_nocb_wake(rcu_state.name, cpu, TPS("Poll"));
> > - schedule_timeout_idle(1);
> > + if (list_empty(&my_rdp->nocb_head_rdp)) {
> > + rcu_wait(READ_ONCE(my_rdp->nocb_toggling_rdp));
> > + } else {
> > + /* Polling, so trace if first poll in the series. */
> > + if (gotcbs)
> > + trace_rcu_nocb_wake(rcu_state.name, cpu, TPS("Poll"));
> > + schedule_timeout_idle(1);
> > + }
> > } else if (!needwait_gp) {
> > /* Wait for callbacks to appear. */
> > trace_rcu_nocb_wake(rcu_state.name, cpu, TPS("Sleep")); @@ -1030,7
> > +1034,7 @@ static long rcu_nocb_rdp_deoffload(void *arg)
> >
> > mutex_lock(&rdp_gp->nocb_gp_kthread_mutex);
> > if (rdp_gp->nocb_gp_kthread) {
> > - if (wake_gp)
> > + if (wake_gp || rcu_nocb_poll)
> > wake_up_process(rdp_gp->nocb_gp_kthread);
> >
> > /*
> > @@ -1152,7 +1156,7 @@ static long rcu_nocb_rdp_offload(void *arg)
> > * rcu_nocb_unlock() rcu_nocb_unlock()
> > */
> > wake_gp = rdp_offload_toggle(rdp, true, flags);
> > - if (wake_gp)
> > + if (wake_gp || rcu_nocb_poll)
> > wake_up_process(rdp_gp->nocb_gp_kthread);
> > swait_event_exclusive(rdp->nocb_state_wq,
> > rcu_segcblist_test_flags(cblist, SEGCBLIST_KTHREAD_CB) &&
> > --
> > 2.25.1
> >
