Messages in this thread |  | | | Date | Wed, 23 Nov 2005 14:13:16 -0800 (PST) | | From | Linus Torvalds <> | | Subject | Re: [patch] SMP alternatives |
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On Wed, 23 Nov 2005, Alan Cox wrote: > > On Mer, 2005-11-23 at 22:13 +0100, Andi Kleen wrote: > > The idea was to turn LOCK on only if the process has any > > shared writable mapping and num_online_cpus() > 0. > > That makes a lot of sense, and if we hit hardware that does funky stuff > then the driver can set a 'vma needs lock' bit for the same effect. > > > Might be a bit costly to rewrite all the page tables for that case > > just to change the PAT index. A bit is nicer for that. > > CPU insert/remove is performed how many times a second ? Or for that > matter why not just reload the PAT register and keep the index the > same ?
It's not about CPU insert/remove.
It's about a single-threaded process becoming multi-threaded, ie a simple "clone()" operation (or doing a shared mmap).
So it needs to be _fast_.
I would strongly argue that it's not a TLB/PAT operation at all. It has nothing to do with the address of the operation. It's a global bit, and it's in the cr3 just because that's what gets reloaded on task switching. But it could be in the CS register too, for all I care..
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