Messages in this thread | | | Date | Thu, 4 Mar 2004 17:14:30 -0500 (EST) | From | Rik van Riel <> | Subject | Re: 2.4.23aa2 (bugfixes and important VM improvements for the high end) |
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On Thu, 4 Mar 2004, Andrea Arcangeli wrote: > On Thu, Mar 04, 2004 at 07:12:23AM -0500, Rik van Riel wrote:
> > All the CPUs use the _same_ mm_struct in kernel space, so > > all VM operations inside the kernel are effectively single > > threaded. > > so what, the 3:1 has the same bottleneck too.
Not true, in the 3:1 split every process has its own mm_struct and they all happen to share the top GB with kernel stuff. You can do a copy_to_user on multiple CPUs efficiently.
> or maybe you mean the page_table_lock hold during copy-user that Andrew > mentioned? (copy-user doesn't mean "all VM operations" not sure if you > meant this or the usual locking of every 2.4/2.6 kernel out there)
True, there are some other operations. However, when you consider the fact that copy-user operations are needed for so many things they are the big bottleneck.
Making it possible to copy things to and from userspace in a lockless way will help performance quite a bit...
-- "Debugging is twice as hard as writing the code in the first place. Therefore, if you write the code as cleverly as possible, you are, by definition, not smart enough to debug it." - Brian W. Kernighan
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