Date: Sat, 16 Jan 1999 22:41:01 -0800 (PST) From: Matthew Dillon <dillon@apollo.backplane.com> To: Terry Lambert <tlambert@primenet.com> Cc: hackers@FreeBSD.ORG Subject: Re: Path to SMP Message-ID: <199901170641.WAA46889@apollo.backplane.com> References: <199901152355.QAA21837@usr04.primenet.com>
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This sounds like it is solving a different problem. It would be
a rather complex solution to a relatively simple problem - processes
can already 'almost' run in supervisor mode, in parallel, in an SMP
environment.
-Matt
:
:Jason Evans has started work on an async call based mechanism.
:
:The functional decomposition is into flags for each system call
:to tell the trap code whether the call will:
:
:(A) Never block
:(B) Sometimes block
:(C) Always block
:
:The kernel work moves the kernel stack into a call context structure,
:which includes a pointer to the VM for the process making the call.
:
:Effectively, this make all entries into the kernel seperately
:schedulable, and allows a process to enter the kernel.
:
:The use of the type-of-call flags is an optimization, allowing the
:use of a "fake" (static, user space) call context structure pointer
:for calls in category (A), or (B), in the case that they run to
:completion instead of blocking.
:
:The mechanism necessitates the addition of a multiplexed system call
:that accepts the commands ACG_WAIT (Async Call Gate Wait) and
:ACG_CANCEL. This is similar to the SVID III aiowait(RT), aiocancel(RT)
:mechanism, and is also similar to the "aio" mechanisms in both
:UnixWare and Solaris, semantically. It's also like the POSIX
:stuff, only with the ability to do all calls, not just some of them.
:
:The mechanism should provide an SMP scalable basis for cooperative
:user and kernel space thread scheduling which fully obeys POSIX
:semantics.
:
:This sidesteps or resolves many of the issues for decomposition,
:as pointed out in:
:
: Scheduling and Load Balancing in Parallel and Distributed
: Systems
:
: Behrooz A. Shirazi, Ali R Hurson, and Krisna M. Kavi
: IEEE Computer Society Press
: ISBN 0-8186-6587-4
:
: Terry Lambert
: terry@lambert.org
:---
:Any opinions in this posting are my own and not those of my present
:or previous employers.
:
:
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:
Matthew Dillon
<dillon@backplane.com>
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