problem with smp and isolcpus

[Samad, Alex]

Hi

This is from the kernel-parameters.txt file in the Documentation
directory

isolcpus=       [KNL,SMP] Isolate CPUs from the general scheduler.
                Format: <cpu number>,...,<cpu number>
                This option can be used to specify one or more CPUs
                to isolate from the general SMP balancing and scheduling
                algorithms. The only way to move a process onto or off
                an "isolated" CPU is via the CPU affinity syscalls.
                <cpu number> begins at 0 and the maximum value is
                "number of CPUs in system - 1".

               This option is the preferred way to isolate CPUs. The
               alternative - manually setting the CPU mask of all tasks
               in the system can cause problems and suboptimal load
               balancer performance.


And from sched.c

/* cpus with isolated domains */
cpumask_t __devinitdata cpu_isolated_map = CPU_MASK_NONE;

/* Setup the mask of cpus configured for isolated domains */
static int __init isolated_cpu_setup(char *str)
{
        int ints[NR_CPUS], i;

        str = get_options(str, ARRAY_SIZE(ints), ints);
        cpus_clear(cpu_isolated_map);
        for (i = 1; i <= ints[0]; i++)
                if (ints[i] < NR_CPUS)
                        cpu_set(ints[i], cpu_isolated_map);
        return 1;
}

__setup ("isolcpus=", isolated_cpu_setup);



I have followed up to see what is happening and why it preffers the
cpu_enabled flag over a kernel parameter 

A

> -----Original Message-----
> From: axp-list-bounces at redhat.com [mailto:axp-list-bounces at redhat.com]
On
> Behalf Of Richard Henderson
> Sent: Friday, 29 July 2005 3:27 PM
> To: Linux on Alpha processors
> Cc: Estabrook, Jay; debian-alpha at lists.debian.org
> Subject: Re: problem with smp and isolcpus
> 
> On Fri, Jul 29, 2005 at 10:43:46AM +1000, Samad, Alex wrote:
> > This brings me to my original question why isn't isolcpus working
when I
> > boot with isolcpus=2 I thought it isolated cpu 2 from the schedular
and
> > thus removed any chance of it running any tasks, threads etc.... Is
this
> > as good as removing it from within srm, or is there a chance that
int's
> > might still run on there.
> 
> No idea what this feature is.
> 
> But if the cpu is bad, you *should* have it completely disabled
> via cpu_enabled.
> 
> 
> r~
> 
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