On Mon, Jun 11, 2007 at 01:44:27PM -0700, Paul E. McKenney wrote:
> On Mon, Jun 11, 2007 at 10:18:06AM -0700, Paul E. McKenney wrote:
> > On Mon, Jun 11, 2007 at 08:55:27AM -0700, Paul E. McKenney wrote:
> > > On Mon, Jun 11, 2007 at 05:38:55PM +0200, Ingo Molnar wrote:
> > > >
> > > > * Paul E. McKenney <[email protected]> wrote:
> > > >
> > > > > > hm, what affinity do they start out with? Could they all be pinned
> > > > > > to CPU#0 by default?
> > > > >
> > > > > They start off with affinity masks of 0xf on a 4-CPU system. I would
> > > > > expect them to load-balance across the four CPUs, but they stay all on
> > > > > the same CPU until long after I lose patience (many minutes).
> > > >
> > > > ugh. Would be nice to figure out why this happens. I enabled rcutorture
> > > > on a dual-core CPU and all the threads are spread evenly.
> > >
> > > Here is the /proc/cpuinfo in case this helps. I am starting up a test
> > > on a dual-core CPU to see if that works better.
> >
> > And this quickly load-balanced to put a pair of readers on each CPU.
> > Later, it moved one of the readers so that it is now running with
> > one reader on one of the CPUs, and the remaining three readers on the
> > other CPU.
> >
> > Argh... this is with 2.6.21-rt1... Need to reboot with 2.6.21.4-rt12...
>
> OK, here are a couple of snapshots from "top" on a two-way system.
> It seems to cycle back and forth between these two states.
And on the 4-CPU box:
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
3112 root 39 19 0 0 0 R 11.6 0.0 0:44.34 rcu_torture_rea
3114 root 39 19 0 0 0 R 11.6 0.0 0:44.34 rcu_torture_rea
3115 root 39 19 0 0 0 R 11.6 0.0 0:44.34 rcu_torture_rea
3116 root 39 19 0 0 0 R 11.6 0.0 0:44.34 rcu_torture_rea
3109 root 39 19 0 0 0 R 11.3 0.0 0:44.33 rcu_torture_rea
3110 root 39 19 0 0 0 R 11.3 0.0 0:44.33 rcu_torture_rea
3111 root 39 19 0 0 0 R 11.3 0.0 0:44.34 rcu_torture_rea
3113 root 39 19 0 0 0 R 11.3 0.0 0:44.34 rcu_torture_rea
3108 root 39 19 0 0 0 D 6.0 0.0 0:24.35 rcu_torture_wri
All are on CPU zero:
elm3b6:~# cat /proc/3109/stat | awk '{print $(NF-3)}'
0
elm3b6:~# cat /proc/3110/stat | awk '{print $(NF-3)}'
0
elm3b6:~# cat /proc/3111/stat | awk '{print $(NF-3)}'
0
elm3b6:~# cat /proc/3112/stat | awk '{print $(NF-3)}'
0
elm3b6:~# cat /proc/3113/stat | awk '{print $(NF-3)}'
0
elm3b6:~# cat /proc/3114/stat | awk '{print $(NF-3)}'
0
elm3b6:~# cat /proc/3115/stat | awk '{print $(NF-3)}'
0
elm3b6:~# cat /proc/3116/stat | awk '{print $(NF-3)}'
0
elm3b6:~# cat /proc/3108/stat | awk '{print $(NF-3)}'
0
All have their affinity masks at f (allowing them to run on all CPUs):
elm3b6:~# taskset -p 3109
pid 3109's current affinity mask: f
elm3b6:~# taskset -p 3110
pid 3110's current affinity mask: f
elm3b6:~# taskset -p 3111
pid 3111's current affinity mask: f
elm3b6:~# taskset -p 3112
pid 3112's current affinity mask: f
elm3b6:~# taskset -p 3113
pid 3113's current affinity mask: f
elm3b6:~# taskset -p 3114
pid 3114's current affinity mask: f
elm3b6:~# taskset -p 3115
pid 3115's current affinity mask: f
elm3b6:~# taskset -p 3116
pid 3116's current affinity mask: f
elm3b6:~# taskset -p 3108
pid 3108's current affinity mask: f
Not a biggie for me, since I can easily do the taskset commands to
force the processes to spread out, but I am worried that casual users
of rcutorture won't know to do this -- thus not really torturing RCU.
It would not be hard to modify rcutorture to affinity the tasks so as
to spread them, but this seems a bit ugly.
Thanx, Paul
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