Re: RCU latency regression in 2.6.16-rc1

From: Paul E. McKenney
Date: Thu Jan 26 2006 - 14:16:55 EST

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On Wed, Jan 25, 2006 at 04:28:25PM -0500, Lee Revell wrote:
> 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)

Dipankar's latest patch should hopefully address this problem.

Could you please give it a spin when you get a chance?

Thanx, Paul
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Next message: Bryan Henderson: "Re: [RFC] VM: I have a dream..."
Previous message: Paul Jackson: "Re: [PATCH 1/6] {set,clear,test}_bit() related cleanup"
In reply to: Lee Revell: "Re: RCU latency regression in 2.6.16-rc1"
Next in thread: Lee Revell: "Re: RCU latency regression in 2.6.16-rc1"
Messages sorted by: [ date ] [ thread ] [ subject ] [ author ]