Re: cpu shielding.

[Serge Hallyn <serge.hallyn-Z7WLFzj8eWMS+FvcfC7Uqw@public.gmane.org>]

Quoting atp (Andrew.Phillips-xheW4WVAX9Y@public.gmane.org):
> Hello,
> 
>   Apologies if I'm about to ask a frequently asked question - I did
> check back over the last couple of months. 
> 
>   Is anyone working on cpu shielding for processes inside a cpu cgroup? 
> 
>   We would like to run Java in containers, and unfortunately it likes to
> know how many processors there are in the system - to initialise thread
> pools and such like. 
> 
>   I was thinking along these lines;
> 
> --- fs/proc/stat.c.orig	2010-05-21 11:32:32.941258466 +0000
> +++ fs/proc/stat.c	2010-05-21 11:40:47.681259133 +0000
> @@ -39,7 +39,9 @@
>  	getboottime(&boottime);
>  	jif = boottime.tv_sec;
>  
> -	for_each_possible_cpu(i) {
> +//	for_each_possible_cpu(i) {
> +//	// refer to the visible cpus.
> +	for_each_cpu_and(i,cpu_possible_mask,(&current->cpus_allowed)) {
>  		user = cputime64_add(user, kstat_cpu(i).cpustat.user);
>  		nice = cputime64_add(nice, kstat_cpu(i).cpustat.nice);
>  		system = cputime64_add(system, kstat_cpu(i).cpustat.system);
> @@ -78,7 +80,10 @@
>  		(unsigned long long)cputime64_to_clock_t(steal),
>  		(unsigned long long)cputime64_to_clock_t(guest),
>  		(unsigned long long)cputime64_to_clock_t(guest_nice));
> -	for_each_online_cpu(i) {
> +     
> +//	for_each_online_cpu(i) {
> +//	// cgroup. 
> +	for_each_cpu_and(i,cpu_online_mask,(&current->cpus_allowed)) {
>  
>  		/* Copy values here to work around gcc-2.95.3, gcc-2.96 */
>  		user = kstat_cpu(i).cpustat.user;
> 
>   I'm sure that there are nicer ways of doing this, but Serge Hallyn
> suggested a while ago that I post here. Even though it says 2010, the
> patch above looks like it will go against 3.2.4 ok. 
>   
>   Thanks,
>      Andy

I'm afraid I haven't been following recent upstream discussions on
this, but there are other people who want proc to show cgroup-limited
information.  See for instance http://lwn.net/Articles/460310/ .  Glauber
has also brought this up since then.  I'd recommend pinging him.

I'm all for /proc showing cgroup-filtered information, unconditionally.

-serge