Date: Wed, 28 Apr 1999 14:48:56 -0700 (PDT) From: Matthew Dillon <dillon@apollo.backplane.com> To: Alan Cox <alc@cs.rice.edu> Cc: Chuck Robey <chuckr@picnic.mat.net>, Poul-Henning Kamp <phk@critter.freebsd.dk>, Luoqi Chen <luoqi@watermarkgroup.com>, current@freebsd.org, smp@freebsd.org Subject: Re: HEADS UP! to commit SMP vmspace sharing patches Message-ID: <199904282148.OAA09354@apollo.backplane.com> References: <Pine.BSF.4.10.9904281400540.378-100000@picnic.mat.net> <199904281819.LAA07937@apollo.backplane.com> <19990428151454.O1121@nonpc.cs.rice.edu>
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:On Wed, Apr 28, 1999 at 11:19:17AM -0700, Matthew Dillon wrote:
:> I know this is a little late ... but I don't suppose there might be a
:> way to lock a TLB entry in place? That would solve the problem too.
:> Baring that, %fs is the way to go.
:>
:
:Unfortunately, on the x86, the answer is "No." The only serious
:alternative was to put the commonly used per processor variables
:and a pointer to the less commonly used ones at the base of each
:process's/thread's kernel stack, i.e., the upages, where you could
:mask off bits from the stack pointer to arrive at the correct address.
:You'd then have to "refresh" most of these variables on a context switch
:(in case the process migrated).
:
: Alan
Too bad.
There might be less confusion with %fs if we simply use it as a
'cpu number' index and then make all the cpu-dependant variables
standard arrays. i.e. instead if 'struct proc *curproc' we would
have 'struct proc *curproc[NCPU];'. The assembly macro would
simply retrieive the current cpu number from %fs, so:
curproc[MYCPU] = ...
This would be much less confusing then trying to encapsulate the concept
of 'curproc', and we could do away with cpu-specific VM areas entirely.
Sure, it would eat a few more cycles, but I don't think it would effect
performance.
-Matt
Matthew Dillon
<dillon@backplane.com>
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