Re: High priority tasks break SMP balancer?

[Dmitry Adamushko]

On 26/11/2007, Micah Dowty <micah@xxxxxxxxxx> wrote:
>
> The application doesn't really depend on the load-balancer's decisions
> per se, it just happens that this behaviour I'm seeing on NUMA systems
> is extremely bad for performance.
>
> In this context, the application is a virtual machine runtime which is
> executing either an SMP VM or it's executing a guest which has a
> virtual GPU. In either case, there are at least three threads:
>
>   - Two virtual CPU/GPU threads, which are nice(0) and often CPU-bound
>   - A low-latency event handling thread, at nice(-10)
>
> The event handling thread performs periodic tasks like delivering
> timer interrupts and completing I/O operations.

Are I/O operations initiated by these "virtual CPU/GPU threads"?

If so, would it make sense to have per-CPU event handling threads
(instead of one global)? They would handle I/O operations initiated
from their respective CPUs to (hopefully) achieve better data locality
(esp. if the most part of the involved data is per-CPU).

Then let the load balancer to evenly distribute the "virtual CPU/GPU
threads" or even (at least, as an experiment) fix them to different
CPUs as well?

sure, the scenario is highly dependent on a nature of those
'events'... and I can just speculate here :-) (but I'd imagine
situations when such a scenario would scale better).


>
> Thank you again,
> --Micah
>

-- 
Best regards,
Dmitry Adamushko
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