Re: SMP Support

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This topic came up yesterday in #l4bsd on freenode, so I'll paste the  
transcript from the general "gist" of the conversation
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[11:12a] rtyler|intel: benno: how does Iguana (and in turn N1  
pistachio) handle SMP?

​​[ snipped intermediate conversation ]

​​[6:28p] ​benno​​: ​rtyler|intel: umm, it handles it just  
fine
​​[6:38p] froody left the chat room. (Read error: 110 (Connection  
timed out))
[6:41p] ggonzahome left the chat room. (Read error: 113 (No route to  
host))
[6:56p] ​rtyler|intel​​: ​benno: I have no doubt about that,  
it's more of a question of how Iguana handles threads and memory in a  
multi-processor environment
​​[6:57p] ​benno​​: ​how exactly do you mean? on smp  
iguana will give you the option of starting threads on different CPUs
​[6:57p] benno: iguana itself will stay single threaded
​[6:58p] benno: (as most of its operations would require holding a  
lock anyway, using IPC as the syncronising method is basically good  
enough..)
​​[6:58p] ​rtyler|intel​​: ​benno: I guess just related to  
how FreeBSD does things (SMPng is my basis for any of this knowledge
​​[6:58p] ​benno​​: ​no idea how freebsd does things
​​[6:58p] ​rtyler|intel​​: ​i.e. 4.xx had the giant lock,  
and SMPng has brought fine-grained locking to 5.xx and 6.xx
​​[6:59p] ​benno​​: ​right, iguana doesn't have fine  
grained locking, its single threadedness is basically a giant lock
​[6:59p] benno: but, you don't really call iguana nearly as often as  
you would call the bsd kernel
​[6:59p] benno: so it isn't clear that fine-grained locking would  
actually buy you anything (and in fact could have worse performance)
​​[6:59p] ​rtyler|intel​​: ​but then what about services  
that it serves? do they share the same giant locking mechanism, in  
regards to the threading that iguana provides
​​[7:00p] ​benno​​: ​well each server running on top of  
iguana can implement the policy it sees best
​[7:00p] benno: but really for most of them, the services then  
selves are fine grained
​[7:00p] benno: so each of these having a giant lock is kind of the  
same as having fine grained locks in a traditional kernel
​[7:01p] benno: well, not fine grained, probably coarse grained, but  
its not like the giant lock
​​[7:01p] ​rtyler|intel​​: ​benno: I guess where i'm  
losing the train of thought is in that Iguana essentially operates as  
a giant lock, and provides threading to it's services, as to how  
those iguana services would run atop SMP systems
​​[7:02p] ​benno​​: ​.. i need a whiteboard...
​[7:02p] benno: it is really L4 providing the smp support
​[7:02p] benno: it provides mechanisms to let you start threads and  
different CPUs
​[7:02p] benno: and migrate threads between different cpus
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Hope that clears things up :)

Cheers,

- -R. Tyler Ballance

On Jun 9, 2006, at 10:32 AM, Michael Emswiler wrote:

> I am interested in Multiprocessor Support in Pistachio.
>
> I was wondering if anyone could point me to a link where i could  
> find current status on SMP support and what's in-progress?
>
> I am primarily interested in EMT64 and AMD64.
>
> Thanks,
> MikeE
>
>

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