Re: UDP-U stream performance regression on 32-rc1 kernel

Zhang, Yanmin
2009-11-05T02:19:56Z

On Wed, 2009-11-04 at 13:07 +0100, Mike Galbraith wrote:
> On Wed, 2009-11-04 at 09:55 +0800, Zhang, Yanmin wrote:
> > On Tue, 2009-11-03 at 18:45 +0100, Ingo Molnar wrote:
> > > * Zhang, Yanmin <yanmin_zhang@linux.intel.com> wrote:
> > >
> > > > On Tue, 2009-11-03 at 11:47 +0800, Alex Shi wrote:
> > > > > We found the UDP-U 1k/4k stream of netperf benchmark have some
> > > > > performance regression from 10% to 20% on our Tulsa and some NHM
> > > > > machines.
> > > > ﻿ perf events shows function find_busiest_group consumes about 4.5% cpu
> > > > time with the patch while it only consumes 0.5% cpu time without the
> > > > patch.
> > > >
> > > > The communication between netperf client and netserver is very fast.
> > > > When netserver receives a message and there is no new message
> > > > available, it goes to sleep and scheduler calls idle_balance =>
> > > > load_balance_newidle. load_balance_newidle spends too much time and a
> > > > new message arrives quickly before load_balance_newidle ends.
> > > >
> > > > As the comments in the patch say hackbench benefits from it, I tested
> > > > hackbench on Nehalem and core2 machines. hackbench does benefit from
> > > > it, about 6% on nehalem machines, but doesn't benefit on core2
> > > > machines.
> > >
> > > Can you confirm that -tip:
> > >
> > > http://people.redhat.com/mingo/tip.git/README
> > >
> > > has it fixed (or at least improved)?
> > The latest tips improves netperf loopback result, but doesn't fix it
> > thoroughly. For example, on a Nehalem machine, netperf UDP-U-1k has
> > about 25% regression, but with the tips kernel, the regression becomes
> > less than 10%.
>

> Can you try the below, and send me
I tested it on Nehalem machine against the latest tips kernel. netperf loopback
result is good and regression disappears.

tbench result has no improvement.

> your UDP-U-1k args so I can try it?
#taskset -c 0 ./netserver
#taskset -c 15 ./netperf -t UDP_STREAM -l 60 -H 127.0.0.1 -i 50 3 -I 99 5 -- -P 12384,12888 -s 32768 -S 32768 -m 4096

Pls. check /proc/cpuinfo to make sure cpu 0 and cpu 15 are not in the
same physical cpu.

I also run sysbench(oltp)+mysql testing with thread number 14,16,18,20,32,64,128. The average
number is good. If I compare every single result against 2.6.32-rc5's, I find thread number
﻿14,16,18,20,32's result are better than 2.6.32-rc5's, but 64,128's result are worse. 128's is
the worst.

>
>
> The below shows promise for stopping newidle from harming cache, though
> it needs to be more clever than a holdoff. The fact that it only harms
> the _very_ sensitive to idle time x264 testcase by 5% shows some
> promise.
>
> tip v2.6.32-rc6-1731-gc5bb4b1
> tbench 8 1044.66 MB/sec 8 procs
> x264 8 366.58 frames/sec -start_debit 392.24 fps -newidle 215.34 fps
>
> tip+ v2.6.32-rc6-1731-gc5bb4b1
> tbench 8 1040.08 MB/sec 8 procs .995
> x264 8 350.23 frames/sec -start_debit 371.76
> .955 .947
>
> mysql+oltp
> clients 1 2 4 8 16 32 64 128 256
> tip 10447.14 19734.58 36038.18 35776.85 34662.76 33682.30 32256.22 28770.99 25323.23
> 10462.61 19580.14 36050.48 35942.63 35054.84 33988.40 32423.89 29259.65 25892.24
> 10501.02 19231.27 36007.03 35985.32 35060.79 33945.47 32400.42 29140.84 25716.16
> tip avg 10470.25 19515.33 36031.89 35901.60 34926.13 33872.05 32360.17 29057.16 25643.87
>
> tip+ 10594.32 19912.01 36320.45 35904.71 35100.37 34003.38 32453.04 28413.57 23871.22
> 10667.96 20000.17 36533.72 36472.19 35371.35 34208.85 32617.80 28893.55 24499.34
> 10463.25 19915.69 36657.20 36419.08 35403.15 34041.80 32612.94 28835.82 24323.52
> tip+ avg 10575.17 19942.62 36503.79 36265.32 35291.62 34084.67 32561.26 28714.31 24231.36
> 1.010 1.021 1.013 1.010 1.010 1.006 1.006 .988 .944
>
>
> ---
> kernel/sched.c | 9 +++++++++
> 1 file changed, 9 insertions(+)
>
> Index: linux-2.6/kernel/sched.c
> ===================================================================
> --- linux-2.6.orig/kernel/sched.c
> +++ linux-2.6/kernel/sched.c
> @@ -590,6 +590,7 @@ struct rq {
>
> u64 rt_avg;
> u64 age_stamp;
> + u64 newidle_ratelimit;
> #endif
>
> /* calc_load related fields */
> @@ -2383,6 +2384,8 @@ static int try_to_wake_up(struct task_st
> if (rq != orig_rq)
> update_rq_clock(rq);
>
> + rq->newidle_ratelimit = rq->clock;
> +
> WARN_ON(p->state != TASK_WAKING);
> cpu = task_cpu(p);
>
> @@ -4427,6 +4430,12 @@ static void idle_balance(int this_cpu, s
> struct sched_domain *sd;
> int pulled_task = 0;
> unsigned long next_balance = jiffies + HZ;
> + u64 delta = this_rq->clock - this_rq->newidle_ratelimit;
> +
> + if (delta < sysctl_sched_migration_cost)
> + return;
> +
> + this_rq->newidle_ratelimit = this_rq->clock;
>
> for_each_domain(this_cpu, sd) {
> unsigned long interval;
>
>
>
>