Re: Intel P6 vs P7 system call performance

From: H. Peter Anvin (
Date: Thu Dec 19 2002 - 14:29:50 EST wrote:
> On 18 Dec, Linus Torvalds wrote:
>>On Wed, 18 Dec 2002, Jamie Lokier wrote:
>>>That said, you always need the page at 0xfffe0000 mapped anyway, so
>>>that sysexit can jump to a fixed address (which is fastest).
>>Yes. This is important. There _needs_ to be some fixed address at least as
>>far as the kernel is concerned (it might move around between reboots or
>>something like that, but it needs to be something the kernel knows about
>>intimately and doesn't need lots of dynamic lookup).
>>However, there's another issue, namely process startup cost. I personally
>>want it to be as light as at all possible. I hate doing an "strace" on
>>user processes and seeing tons and tons of crapola showing up. Just for
> So why not map the magic page at 0xffffe000 at some other address as
> well?
> Static binaries can just directly jump/call into the magic page.
> Shared binaries do somekind of mmap("/proc/self/mem") magic to put a
> copy of the page at an address that is convenient for them. Shared
> binaries have to do a lot of mmap-ing anyway, so the overhead should be
> negligible.

That would require /proc to be mounted for all shared binaries to work.
 That is tantamount to killing chroot().

Perhaps it could be done with mremap(), but I would assume that would
entail a special case in the mremap() code.

A special system call would be a bit gross, but it's better than a total


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