Multi-core programming

Wouldn't that be rather 360 specific? In the regular .net framework you can set affinity and priority on a thread, isn't that sufficient? Or does the XNA framework introduce a new way of dealing with threads?

Does the lock and volatile keyword work the same on the 360?

Thanks,

Roger Larsen

twospoons at 2007-8-30 >

explicit model: you tell the OS which core each thread should run on,

and then the OS keeps out the way and leaves you to it. Wheras on

Windows the OS is far more sophisticated (and heavyweight) doing all

sorts of automatic allocation behind the scenes even if you don't

specify an explicit affinity.

We figured that since the underlying OS concepts are quite different,

and anyone writing multithreaded code probably cares enough about

performance that these differences are going to be important for them,

it didn't really make sense to try to make affinity look the same on

the both platforms. It will be similar, but even tiny differences can

be important for that sort of code!

ShawnHargreaves at 2007-8-30 >

Shawn Hargreaves wrote:

Xbox threading is somewhat different to on Windows. It is a much more explicit model: you tell the OS which core each thread should run on, and then the OS keeps out the way and leaves you to it. Wheras on Windows the OS is far more sophisticated (and heavyweight) doing all sorts of automatic allocation behind the scenes even if you don't specify an explicit affinity. We figured that since the underlying OS concepts are quite different, and anyone writing multithreaded code probably cares enough about performance that these differences are going to be important for them, it didn't really make sense to try to make affinity look the same on the both platforms. It will be similar, but even tiny differences can be important for that sort of code!

So basically you need different code blocks for different platforms. Does the kernel still schedule the threads, or is it more of a fiber approach? I'm more worried about volatile and locks, if they behave diffrently then we will have issues.

Roger Larsen

twospoons at 2007-8-30 >

twospoons wrote:

So basically you need different code blocks for different platforms. Does the kernel still schedule the threads, or is it more of a fiber approach? I'm more worried about volatile and locks, if they behave diffrently then we will have issues.

The Xbox kernel schedules threads preemptively, but I'm pretty sure it

won't reallocate them from one core to another. You often won't need to

care about the differences from Windows: it is only when writing super

optimized parallised game engines that these subtleties can become

important.

Volatile and locks will follow the standard CLR behavior.

ShawnHargreaves at 2007-8-30 >

twospoons wrote:

Does all the cores share the same L2 cache (Core 2 Duo style)? Does the hardware threads on each core share the same L2 cache? Sorry for all the questions, but if you have some docs to point me to I'll read those instead :)

There is a single shared L2 cache. Each of the three cores has its own

L1 cache, which is shared between the two hardware threads on that core.

http://www-128.ibm.com/developerworks/power/library/pa-fpfxbox/ has

some more details. Ars Technica also did a gory low level article on

the 360 CPU, but it seems to be subscribers only.

ShawnHargreaves at 2007-8-30 >