Re: RCU latency regression in 2.6.16-rc1
From: Lee Revell
Date: Wed Jan 25 2006 - 16:26:48 EST
On Wed, 2006-01-25 at 03:08 +0530, Dipankar Sarma wrote:
> On Tue, Jan 24, 2006 at 09:58:46PM +0530, Dipankar Sarma wrote:
> > On Tue, Jan 24, 2006 at 04:44:15AM -0500, Lee Revell wrote:
> > > On Tue, 2006-01-24 at 10:23 +0100, Ingo Molnar wrote:
> > > > * Paul E. McKenney <paulmck@xxxxxxxxxx> wrote:
> > > >
> > > > > This patch was primarily designed to reduce memory overhead, but given
> > > > > that it tends to reduce batch size, it should also reduce latency.
> > > >
> > > > if this solves Lee's problem, i think we should apply this as a fix, and
> > > > get it into v2.6.16. The patch looks straightforward and correct to me.
> > > >
> > >
> > > Does not compile:
> > >
> > > CC kernel/rcupdate.o
> > > kernel/rcupdate.c:76: warning: 'struct rcu_state' declared inside parameter list
> >
> > My original patch was against a much older kernel.
> > I will send out a more uptodate patch as soon as I am done with some
> > testing.
>
> Here is an updated version of that patch against 2.6.16-rc1. I have
> sanity-tested it on ppc64 and x86_64 using dbench and kernbench.
> I have also tested this for OOM situations - open()/close() in
> a tight loop in my x86_64 which earlier used to reach file limit
> if I set batch limit to 10 and found no problem. This patch does set
> default RCU batch limit to 10 and changes it only when there is an RCU
> flood.
OK this seems to work, I can't tell yet whether it help the latency I
reported, but rt_run_flush still produces terrible latencies.
Ingo, should I try the softirq preemption patch + Dipankar's patch +
latency tracing patch?
preemption latency trace v1.1.5 on 2.6.16-rc1
--------------------------------------------------------------------
latency: 7418 us, #6397/6397, CPU#0 | (M:rt VP:0, KP:0, SP:0 HP:0)
-----------------
| task: gmplayer-8638 (uid:1000 nice:-20 policy:0 rt_prio:0)
-----------------
_------=> CPU#
/ _-----=> irqs-off
| / _----=> need-resched
|| / _---=> hardirq/softirq
||| / _--=> preempt-depth
|||| /
||||| delay
cmd pid ||||| time | caller
\ / ||||| \ | /
Xorg-2154 0d.s2 1us : __trace_start_sched_wakeup (try_to_wake_up)
Xorg-2154 0d.s2 2us : __trace_start_sched_wakeup <<...>-8638> (64 0)
Xorg-2154 0d.s. 3us+: wake_up_process (hrtimer_run_queues)
Xorg-2154 0d.s. 6us : rt_secret_rebuild (run_timer_softirq)
Xorg-2154 0d.s. 7us : rt_cache_flush (rt_secret_rebuild)
Xorg-2154 0d.s1 7us : del_timer (rt_cache_flush)
Xorg-2154 0d.s. 9us : local_bh_enable (rt_cache_flush)
Xorg-2154 0d.s. 10us : rt_run_flush (rt_cache_flush)
Xorg-2154 0d.s. 11us : get_random_bytes (rt_run_flush)
Xorg-2154 0d.s. 12us : extract_entropy (get_random_bytes)
Xorg-2154 0d.s. 13us : xfer_secondary_pool (extract_entropy)
Xorg-2154 0d.s. 15us : extract_entropy (xfer_secondary_pool)
Xorg-2154 0d.s. 16us : xfer_secondary_pool (extract_entropy)
Xorg-2154 0d.s. 17us+: account (extract_entropy)
Xorg-2154 0d.s. 19us : extract_buf (extract_entropy)
Xorg-2154 0d.s. 20us : sha_init (extract_buf)
Xorg-2154 0d.s. 21us+: sha_transform (extract_buf)
Xorg-2154 0d.s. 29us+: __add_entropy_words (extract_buf)
Xorg-2154 0d.s. 32us+: sha_transform (extract_buf)
Xorg-2154 0d.s. 39us : __add_entropy_words (extract_buf)
Xorg-2154 0d.s. 40us+: sha_transform (extract_buf)
Xorg-2154 0d.s. 47us : __add_entropy_words (extract_buf)
Xorg-2154 0d.s. 48us+: sha_transform (extract_buf)
Xorg-2154 0d.s. 55us : __add_entropy_words (extract_buf)
Xorg-2154 0d.s. 56us+: sha_transform (extract_buf)
Xorg-2154 0d.s. 63us : __add_entropy_words (extract_buf)
Xorg-2154 0d.s. 64us+: sha_transform (extract_buf)
Xorg-2154 0d.s. 71us : __add_entropy_words (extract_buf)
Xorg-2154 0d.s. 73us+: sha_transform (extract_buf)
Xorg-2154 0d.s. 79us : __add_entropy_words (extract_buf)
Xorg-2154 0d.s. 81us+: sha_transform (extract_buf)
Xorg-2154 0d.s. 87us : __add_entropy_words (extract_buf)
Xorg-2154 0d.s. 81us+: sha_transform (extract_buf)
Xorg-2154 0d.s. 87us : __add_entropy_words (extract_buf)
Xorg-2154 0d.s. 89us : __add_entropy_words (extract_buf)
Xorg-2154 0d.s. 91us+: sha_transform (extract_buf)
Xorg-2154 0d.s. 98us : __add_entropy_words (xfer_secondary_pool)
Xorg-2154 0d.s. 100us : credit_entropy_store (xfer_secondary_pool)
Xorg-2154 0d.s. 101us : account (extract_entropy)
Xorg-2154 0d.s1 102us : __wake_up (account)
Xorg-2154 0d.s2 103us : __wake_up_common (__wake_up)
Xorg-2154 0d.s. 104us : extract_buf (extract_entropy)
Xorg-2154 0d.s. 105us : sha_init (extract_buf)
Xorg-2154 0d.s. 106us+: sha_transform (extract_buf)
Xorg-2154 0d.s. 113us : __add_entropy_words (extract_buf)
Xorg-2154 0d.s. 114us+: sha_transform (extract_buf)
Xorg-2154 0d.s. 121us : __add_entropy_words (extract_buf)
Xorg-2154 0d.s. 122us : __add_entropy_words (extract_buf)
Xorg-2154 0d.s. 124us+: sha_transform (extract_buf)
Xorg-2154 0d.s. 132us : local_bh_enable (rt_run_flush)
Xorg-2154 0d.s. 133us : local_bh_enable (rt_run_flush)
Xorg-2154 0d.s. 134us : local_bh_enable (rt_run_flush)
Xorg-2154 0d.s. 135us : local_bh_enable (rt_run_flush)
Xorg-2154 0d.s. 136us : local_bh_enable (rt_run_flush)
Xorg-2154 0d.s. 137us : local_bh_enable (rt_run_flush)
Xorg-2154 0d.s. 139us : local_bh_enable (rt_run_flush)
Xorg-2154 0d.s. 140us : local_bh_enable (rt_run_flush)
Xorg-2154 0d.s. 141us : local_bh_enable (rt_run_flush)
Xorg-2154 0d.s. 142us : local_bh_enable (rt_run_flush)
Xorg-2154 0d.s. 143us : local_bh_enable (rt_run_flush)
Xorg-2154 0d.s. 145us : local_bh_enable (rt_run_flush)
Xorg-2154 0d.s. 146us : call_rcu_bh (rt_run_flush)
Xorg-2154 0d.s. 148us : local_bh_enable (rt_run_flush)
Xorg-2154 0d.s. 149us : local_bh_enable (rt_run_flush)
Xorg-2154 0d.s. 150us : local_bh_enable (rt_run_flush)
Xorg-2154 0d.s. 151us : local_bh_enable (rt_run_flush)
Xorg-2154 0d.s. 152us : local_bh_enable (rt_run_flush)
Xorg-2154 0d.s. 154us : local_bh_enable (rt_run_flush)
Xorg-2154 0d.s. 155us : local_bh_enable (rt_run_flush)
Xorg-2154 0d.s. 156us : local_bh_enable (rt_run_flush)
Xorg-2154 0d.s. 157us : local_bh_enable (rt_run_flush)
Xorg-2154 0d.s. 158us : local_bh_enable (rt_run_flush)
Xorg-2154 0d.s. 159us : local_bh_enable (rt_run_flush)
Xorg-2154 0d.s. 161us : local_bh_enable (rt_run_flush)
Xorg-2154 0d.s. 162us : local_bh_enable (rt_run_flush)
Xorg-2154 0d.s. 163us : local_bh_enable (rt_run_flush)
Xorg-2154 0d.s. 164us : call_rcu_bh (rt_run_flush)
Xorg-2154 0d.s. 166us : local_bh_enable (rt_run_flush)
Xorg-2154 0d.s. 167us : local_bh_enable (rt_run_flush)
Xorg-2154 0d.s. 168us : local_bh_enable (rt_run_flush)
Xorg-2154 0d.s. 169us : local_bh_enable (rt_run_flush)
Xorg-2154 0d.s. 170us : local_bh_enable (rt_run_flush)
Xorg-2154 0d.s. 172us : call_rcu_bh (rt_run_flush)
Xorg-2154 0d.s. 173us : local_bh_enable (rt_run_flush)
Xorg-2154 0d.s. 174us : local_bh_enable (rt_run_flush)
Xorg-2154 0d.s. 175us : local_bh_enable (rt_run_flush)
Xorg-2154 0d.s. 176us : local_bh_enable (rt_run_flush)
Xorg-2154 0d.s. 178us : call_rcu_bh (rt_run_flush)
Xorg-2154 0d.s. 179us : local_bh_enable (rt_run_flush)
Xorg-2154 0d.s. 180us : local_bh_enable (rt_run_flush)
Xorg-2154 0d.s. 181us : call_rcu_bh (rt_run_flush)
Xorg-2154 0d.s. 182us : call_rcu_bh (rt_run_flush)
Xorg-2154 0d.s. 184us : local_bh_enable (rt_run_flush)
Xorg-2154 0d.s. 185us : call_rcu_bh (rt_run_flush)
Xorg-2154 0d.s. 186us : local_bh_enable (rt_run_flush)
Xorg-2154 0d.s. 187us : local_bh_enable (rt_run_flush)
Xorg-2154 0d.s. 188us : local_bh_enable (rt_run_flush)
Xorg-2154 0d.s. 190us : local_bh_enable (rt_run_flush)
Xorg-2154 0d.s. 191us : call_rcu_bh (rt_run_flush)
Xorg-2154 0d.s. 192us : call_rcu_bh (rt_run_flush)
Xorg-2154 0d.s. 193us : local_bh_enable (rt_run_flush)
Xorg-2154 0d.s. 194us : local_bh_enable (rt_run_flush)
Xorg-2154 0d.s. 195us : call_rcu_bh (rt_run_flush)
Xorg-2154 0d.s. 197us : local_bh_enable (rt_run_flush)
Xorg-2154 0d.s. 198us : local_bh_enable (rt_run_flush)
Xorg-2154 0d.s. 199us : call_rcu_bh (rt_run_flush)
Xorg-2154 0d.s. 200us : local_bh_enable (rt_run_flush)
Xorg-2154 0d.s. 201us : local_bh_enable (rt_run_flush)
Xorg-2154 0d.s. 202us : local_bh_enable (rt_run_flush)
Xorg-2154 0d.s. 204us : local_bh_enable (rt_run_flush)
Xorg-2154 0d.s. 205us : local_bh_enable (rt_run_flush)
Xorg-2154 0d.s. 206us : local_bh_enable (rt_run_flush)
Xorg-2154 0d.s. 207us : local_bh_enable (rt_run_flush)
Xorg-2154 0d.s. 208us : call_rcu_bh (rt_run_flush)
Xorg-2154 0d.s. 210us : local_bh_enable (rt_run_flush)
Xorg-2154 0d.s. 211us : local_bh_enable (rt_run_flush)
Xorg-2154 0d.s. 212us : local_bh_enable (rt_run_flush)
Xorg-2154 0d.s. 213us : call_rcu_bh (rt_run_flush)
Xorg-2154 0d.s. 215us : local_bh_enable (rt_run_flush)
Xorg-2154 0d.s. 216us : local_bh_enable (rt_run_flush)
Xorg-2154 0d.s. 217us : local_bh_enable (rt_run_flush)
Xorg-2154 0d.s. 218us : local_bh_enable (rt_run_flush)
Xorg-2154 0d.s. 219us : local_bh_enable (rt_run_flush)
Xorg-2154 0d.s. 220us : local_bh_enable (rt_run_flush)
Xorg-2154 0d.s. 222us : local_bh_enable (rt_run_flush)
Xorg-2154 0d.s. 223us : call_rcu_bh (rt_run_flush)
[ zillions of these deleted ]
Xorg-2154 0d.s. 7335us : local_bh_enable (rt_run_flush)
Xorg-2154 0d.s. 7336us : local_bh_enable (rt_run_flush)
Xorg-2154 0d.s. 7337us : local_bh_enable (rt_run_flush)
Xorg-2154 0d.s. 7339us : local_bh_enable (rt_run_flush)
Xorg-2154 0d.s. 7340us : local_bh_enable (rt_run_flush)
Xorg-2154 0d.s. 7341us : local_bh_enable (rt_run_flush)
Xorg-2154 0d.s. 7342us : call_rcu_bh (rt_run_flush)
Xorg-2154 0d.s. 7343us : local_bh_enable (rt_run_flush)
Xorg-2154 0d.s. 7344us : local_bh_enable (rt_run_flush)
Xorg-2154 0d.s. 7346us : mod_timer (rt_secret_rebuild)
Xorg-2154 0d.s. 7346us : __mod_timer (mod_timer)
Xorg-2154 0d.s. 7347us : lock_timer_base (__mod_timer)
Xorg-2154 0d.s1 7348us+: internal_add_timer (__mod_timer)
Xorg-2154 0d.s. 7350us : run_timer_softirq (__do_softirq)
Xorg-2154 0d.s. 7351us : hrtimer_run_queues (run_timer_softirq)
Xorg-2154 0d.s. 7352us : ktime_get_real (hrtimer_run_queues)
Xorg-2154 0d.s. 7352us : getnstimeofday (ktime_get_real)
Xorg-2154 0d.s. 7353us : do_gettimeofday (getnstimeofday)
Xorg-2154 0d.s. 7353us : get_offset_tsc (do_gettimeofday)
Xorg-2154 0d.s. 7355us : ktime_get (hrtimer_run_queues)
Xorg-2154 0d.s. 7355us : ktime_get_ts (ktime_get)
Xorg-2154 0d.s. 7356us : getnstimeofday (ktime_get_ts)
Xorg-2154 0d.s. 7357us : do_gettimeofday (getnstimeofday)
Xorg-2154 0d.s. 7357us : get_offset_tsc (do_gettimeofday)
Xorg-2154 0d.s. 7358us : set_normalized_timespec (ktime_get_ts)
Xorg-2154 0d.s1 7359us : __remove_hrtimer (hrtimer_run_queues)
Xorg-2154 0d.s1 7360us : rb_next (__remove_hrtimer)
Xorg-2154 0d.s1 7361us : rb_erase (__remove_hrtimer)
Xorg-2154 0d.s. 7362us : it_real_fn (hrtimer_run_queues)
Xorg-2154 0d.s. 7363us : send_group_sig_info (it_real_fn)
Xorg-2154 0d.s1 7364us : group_send_sig_info (send_group_sig_info)
Xorg-2154 0d.s1 7365us : check_kill_permission (group_send_sig_info)
Xorg-2154 0d.s1 7367us : dummy_task_kill (check_kill_permission)
Xorg-2154 0d.s2 7369us : __group_send_sig_info (group_send_sig_info)
Xorg-2154 0d.s2 7369us : handle_stop_signal (__group_send_sig_info)
Xorg-2154 0d.s2 7371us : sig_ignored (__group_send_sig_info)
Xorg-2154 0d.s2 7372us : send_signal (__group_send_sig_info)
Xorg-2154 0d.s2 7373us : __sigqueue_alloc (send_signal)
Xorg-2154 0d.s2 7374us+: kmem_cache_alloc (__sigqueue_alloc)
Xorg-2154 0d.s2 7377us : __group_complete_signal (__group_send_sig_info)
Xorg-2154 0d.s2 7378us : task_curr (__group_complete_signal)
Xorg-2154 0d.s2 7379us : signal_wake_up (__group_complete_signal)
Xorg-2154 0d.s2 7380us : wake_up_state (signal_wake_up)
Xorg-2154 0d.s2 7380us : try_to_wake_up (wake_up_state)
Xorg-2154 0d.s2 7381us : wake_up_state (signal_wake_up)
Xorg-2154 0d.s. 7382us : hrtimer_forward (it_real_fn)
Xorg-2154 0d.s. 7383us : ktime_get (hrtimer_forward)
Xorg-2154 0d.s. 7383us : ktime_get_ts (ktime_get)
Xorg-2154 0d.s. 7384us : getnstimeofday (ktime_get_ts)
Xorg-2154 0d.s. 7385us : do_gettimeofday (getnstimeofday)
Xorg-2154 0d.s. 7385us : get_offset_tsc (do_gettimeofday)
Xorg-2154 0d.s. 7386us : set_normalized_timespec (ktime_get_ts)
Xorg-2154 0d.s1 7388us : enqueue_hrtimer (hrtimer_run_queues)
Xorg-2154 0d.s1 7389us : rb_insert_color (enqueue_hrtimer)
Xorg-2154 0d.s. 7390us : tasklet_action (__do_softirq)
Xorg-2154 0d.s. 7391us : rcu_process_callbacks (tasklet_action)
Xorg-2154 0d.s. 7392us : __rcu_process_callbacks (rcu_process_callbacks)
Xorg-2154 0d.s. 7393us : __rcu_process_callbacks (rcu_process_callbacks)
Xorg-2154 0d.s1 7394us+: rcu_start_batch (__rcu_process_callbacks)
Xorg-2154 0dn.. 7397us : schedule (work_resched)
Xorg-2154 0dn.. 7397us : stop_trace (schedule)
Xorg-2154 0dn.. 7398us : profile_hit (schedule)
Xorg-2154 0dn.1 7399us+: sched_clock (schedule)
Xorg-2154 0dn.2 7402us : recalc_task_prio (schedule)
Xorg-2154 0dn.2 7403us : effective_prio (recalc_task_prio)
Xorg-2154 0dn.2 7404us+: requeue_task (schedule)
<...>-8638 0d..2 7410us+: __switch_to (schedule)
<...>-8638 0d..2 7414us : schedule <Xorg-2154> (74 64)
<...>-8638 0d..1 7414us : trace_stop_sched_switched (schedule)
<...>-8638 0d..2 7415us : trace_stop_sched_switched <<...>-8638> (64 0)
<...>-8638 0d..2 7417us : schedule (schedule)
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/