process scheduling and cpuset

[Dmitry Sivachenko]

> On 13 сент. 2015 г., at 16:09, Slawa Olhovchenkov <slw at zxy.spb.ru> wrote:
> 
> On Sun, Sep 13, 2015 at 02:52:08PM +0300, Dmitry Sivachenko wrote:
> 
>> Hello,
>> 
>> I have 32 processor machine (2x CPU E5-2650) running several CPU-bound processes (ULE scheduler).
>> 3 processes are 32-threaded, and 8 are single threaded.
>> 
>> I bind all 3 32-threaded processes to CPUs 0-24 (cpuset -C -l 0-24 -p XXX).
>> 
>> I expect that the remaining 8 single-threaded processes will (mostly) run on the remaining 25-31 CPU cores and use (almost) 100% cpu each.
>> 
>> But this is not the case (according to top(1)):  they spend a lot of time on 0-24 CPUs and CPU Idle time is about 10%.
>> 
>> These are all purely computational programs, in idle system single-threaded programs steadily consume 100% of a core, and 32-threaded programs consume all 32 cores and idle time is zero.
>> 
>> Is it an ULE scheduler feature or am I doing something wrong?
>> 
>> The goal is to give a single-threaded program a chance to run when somebody started several 32-threaded processes.
> 
> You don't have 32 processor machine, you have only 16 processor
> machine.
> SMT/hyperthreading don't give real processor, SMT "CPU" have
> unpredicable power and his load depend on load parent CPU.
> 
> For example, for my case I see such condition (simpliy) on CPU 0 and 1
> (SMT of one real core) with rise load:
> 
> load 0.1  0.1
> load 0.2  0.2
> load 0.3  0.3
> load 0.4  0.4
> load 0.45 0.45
> load 0.48 0.48
> load 1.00 1.00\


Yes I know about HT.  But how does this explain why I have 10% of CPU idle?

If I explicitly bind my single-threaded processes to the remaining CPU cores (25-32), they start to receive expected 100% of CPU and overall Idle decreases.

I just expect scheduler to do the same for me.