Date: Sun, 15 Dec 1996 11:28:31 -0500 (EST) From: "John S. Dyson" <toor@dyson.iquest.net> To: phk@critter.tfs.com (Poul-Henning Kamp) Cc: peter@spinner.dialix.com, dyson@freebsd.org, smp@freebsd.org, haertel@ichips.intel.com Subject: Re: some questions concerning TLB shootdowns in FreeBSD Message-ID: <199612151628.LAA05010@dyson.iquest.net> In-Reply-To: <9319.850645034@critter.tfs.com> from "Poul-Henning Kamp" at Dec 15, 96 11:17:14 am
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>
> In message <199612151003.SAA14741@spinner.DIALix.COM>, Peter Wemm writes:
> >Poul-Henning Kamp wrote:
> >> In message <199612150121.JAA12763@spinner.DIALix.COM>, Peter Wemm writes:
> >>
> >> >However, the shared address space code that I was working on in
> >> >-current (for kernel assisted threading in the smp kernel) means
> >> >that a single vmspace/pmap/etc can be shared among multiple processes
> >> >and this changes the above picture since two cpu's can be using
> >> >the user mode parts of the same page tables at once, one in executing
> >> >in user mode, one in the kernel.
> >>
> >> But we could still have a per-cpu flags:
> >> "I'm not in a shared address-space"
> >>
> >> Ie, this would only be set if the CPU was in userland in a non-threaded
> >> process.
> >
> >eg, something like:
> >if (is_userland && curproc->p_vmspace->vm_refcnt > 1)
> > send_tlb_invalidate();
>
> Well more like:
>
> for (i=0;i<NCPU;i++)
> if (is_userland(i) && curproc[i]->p_vmspace->vm_refcnt > 1)
> send_tlb_invalidate(i);
>
This won't work because processes seldom have the entire address space
shared (vm_refcnt.) I am sure that when we get true kernel multithreading
that will not be true though. In order to test if a section of an
address space is shared, you have to do something like this (and
this can take LOTS of time.) (I might have levels of indirection
off here, I am also not taking into account submaps -- which
complicate the code further, by entailing recursively calling
the map/object traversal again -- but recursion is a major
no-no in the kernel, as we have found.)
for(i=0;i<NCPU;i++) {
tmpe = &curproc[i]->p_vmspace->vm_map->header.next;
while (tmpe != &map->header) {
if ((tmpe->is_sub_map == 0) && (tmpe->is_a_map == 0)) {
tobj = tmpe->object.vm_object;
while(tobj) {
if (tobj->ref_count > 1) {
send_tlb_invalidate(i);
goto nextcpu;
}
tobj = tobj->backing_object;
}
} else {
/*
* here on a new map -- need to recurse or
* somesuch here -- yuck!!!
*/
}
tmpe = tmpe->next;
}
nextcpu:
}
John
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