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:

quoted

On Mon, Jun 11, 2007 at 08:55:27AM -0700, Paul E. McKenney wrote:

quoted

On Mon, Jun 11, 2007 at 05:38:55PM +0200, Ingo Molnar wrote:

quoted

* Paul E. McKenney [off-list ref] wrote:

quoted

quoted

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