Re: detecting hyperthreading in linux 2.4.19

[Mark Hounschell <markh@compro.net>]

Jason Lunz wrote:
> 
> jamesclv@us.ibm.com said:
> > I don't know of any way to do this in userland.  The whole point is
> > that the sibling processors are supposed to look like real ones.
> 
> That's unfortunately not always true. I'm writing a program that will
> run on a system that will be doing high-load routing. Testing has shown
> that we get better performance when binding each NIC's interrupts to a
> separate physical processor using /proc/irq/*/smp_affinity (especially
> when all the interrupts would hit the first CPU, another problem i've
> yet to address). That only works for real processors, though, not
> HT siblings.

Strange, I'm doing the very same thing (not with NICs though) using the
local_irq_desc
at the driver level or via /proc/irq/*/smp_affinity method and both work fine.
2.4.18 and 2.4.20 both work here but haven't actually used 2.4.19.
 
> 
> I'm writing a program to run on machines of unknown (by me)
> configuration, that will spread out the NIC interrupts appropriately.
> So userspace needs to know the difference, at least until interrupts can
> be automatically distributed by the kernel in a satisfactory way.

My userland app doesn't know the difference and works fine whether HT or not.
At least according to /proc/interrupts, xosview, and the actual performance of
my app.

Mark