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Date: Sun, 7 Jul 2002 17:33:27 -0500
From: Alan Cox <alc@cs.rice.edu>
To: Matthew Dillon <dillon@apollo.backplane.com>
Cc: Peter Wemm <peter@wemm.org>, Jake Burkholder <jake@locore.ca>,
	Alan Cox <alc@FreeBSD.ORG>, cvs-committers@FreeBSD.ORG,
	cvs-all@FreeBSD.ORG
Subject: Re: cvs commit: src/sys/vm vm_zeroidle.c
Message-ID: <20020707223327.GB11391@cs.rice.edu>
References: <20020707211530.GZ11391@cs.rice.edu> <20020707212707.BD3713808@overcee.wemm.org> <20020707213541.GA11391@cs.rice.edu> <200207072226.g67MQqoT017816@apollo.backplane.com>
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On Sun, Jul 07, 2002 at 03:26:52PM -0700, Matthew Dillon wrote:
> 
> :> Thats what I did to avoid reentrancy problems.  The zeroidle process uses
> :> CMAP3 on x86.  (ugh! why not allocate some kvm? hmmm).
> :> 
> :> However, with preemption, we can end up on another cpu.  Or, we get
> :> scheduled on a different cpu next time.  If we had a way to pin a khread to
> :> a particular cpu, now that would be nice.  We could get in, pin ourselves,
> :> do our mappings, zero the page, unmap, unpin and done.  No preemption
> :> problems to worry about then, and no need to worry about coherency on other
> :> cpus since this is explicitly single threaded.
> :
> :Let me suggest another way to deal with preemption: associate a flag
> :with the pmap that says flush the TLB on activation even if you
> :appear to be switching to the same page table, in this case the kernel's
> :page table.  pmap_zero_page() would set and unset this flag around
> :the bzero().
> :
> :Alan
> 
>     You mean CMAP2, not CMAP3, I think.
> 

Peter's patch adds a CMAP3, which is essentially a private KVA
for pmap_zero_page().

Alan

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