Re: [PATCH for mm] Remove iBCS support

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To: David Newall <davidn@...>
Cc: Andi Kleen <andi@...>, <akpm@...>, <linux-kernel@...>
Date: Sunday, January 20, 2008 - 1:55 am

On Sun, Jan 20, 2008 at 04:03:22PM +1030, David Newall wrote:

Well I'm sure if they migrate they can either recompile or pay someone
to forward port and apply and support the iBCS emulation patchkit.
And for that person it will be only a few minutes to readd these hunks.

However it doesn't make any sense to have all Linux systems ever
out there who can't even run these binaries without significantly
changing the kernel have carry the overhead of these unnecessary checks.


I'm not sure the cost is that low because they access one (or more likely
two) out of line data cache line for the two strings and kernel often runs
cache cold because userland tends to fill the caches and then a cache miss
can be actually hundreds of cycles, possibly multiplied by two.

But assuming there is no cache miss (which is a very conservative
assumption) and the strcmps cost 20 cycles and you got 1 million
2Ghz Linux systems out there doing 100k execs each day we're talking
about 1000 CPU seconds wasted each day. That should be certainly
measurable on most stop watches.


They have to patch the kernel in non trivial ways anyways because they
would need to patch in the whole old iBCS emulation layer.

(e.g. the old default ldt code which was for iBCS was just dropped --
strangely you didn't raise your voice against that)


Sorry, but I don't think you know what you're talking about here.

-Andi

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Messages in current thread:
[PATCH for mm] Remove iBCS support, Andi Kleen, (Sat Jan 19, 12:59 am)
Re: [PATCH for mm] Remove iBCS support, Ingo Molnar, (Fri Jan 25, 8:17 am)
Re: [PATCH for mm] Remove iBCS support, David Newall, (Sat Jan 19, 10:27 pm)
Re: [PATCH for mm] Remove iBCS support, Andi Kleen, (Sat Jan 19, 11:11 pm)
Re: [PATCH for mm] Remove iBCS support, David Newall, (Sun Jan 20, 12:46 am)
Re: [PATCH for mm] Remove iBCS support, Andi Kleen, (Sun Jan 20, 1:18 am)
Re: [PATCH for mm] Remove iBCS support, David Newall, (Sun Jan 20, 1:33 am)
Re: [PATCH for mm] Remove iBCS support, Alan Cox, (Sun Jan 20, 9:06 am)
Re: [PATCH for mm] Remove iBCS support, David Newall, (Sun Jan 20, 9:43 am)
Re: [PATCH for mm] Remove iBCS support, Alan Cox, (Sun Jan 20, 9:51 am)
Re: [PATCH for mm] Remove iBCS support, Andi Kleen, (Sun Jan 20, 1:55 am)
Re: [PATCH for mm] Remove iBCS support, David Newall, (Sun Jan 20, 2:23 am)
Re: [PATCH for mm] Remove iBCS support, Andi Kleen, (Sun Jan 20, 3:29 am)
Re: [PATCH for mm] Remove iBCS support, David Newall, (Sun Jan 20, 9:37 pm)
Re: [PATCH for mm] Remove iBCS support, Ingo Molnar, (Tue Jan 22, 7:12 am)
Re: [PATCH for mm] Remove iBCS support, David Newall, (Tue Jan 22, 11:13 am)
Re: [PATCH for mm] Remove iBCS support, Alan Cox, (Tue Jan 22, 12:50 pm)
Re: [PATCH for mm] Remove iBCS support, David Newall, (Thu Jan 24, 1:08 pm)
Re: [PATCH for mm] Remove iBCS support, Adrian Bunk, (Tue Jan 22, 12:01 pm)
Re: [PATCH for mm] Remove iBCS support, David Newall, (Thu Jan 24, 1:04 pm)
Re: [PATCH for mm] Remove iBCS support, Adrian Bunk, (Thu Jan 24, 1:24 pm)
Re: [PATCH for mm] Remove iBCS support, David Newall, (Thu Jan 24, 1:55 pm)
Re: [PATCH for mm] Remove iBCS support, Pavel Machek, (Thu Jan 24, 3:51 pm)
Re: [PATCH for mm] Remove iBCS support, David Newall, (Thu Jan 24, 10:17 pm)
Re: [PATCH for mm] Remove iBCS support, Andi Kleen, (Thu Jan 24, 4:37 pm)
Re: [PATCH for mm] Remove iBCS support, David Newall, (Thu Jan 24, 10:16 pm)
Re: [PATCH for mm] Remove iBCS support, Adrian Bunk, (Thu Jan 24, 2:14 pm)
Re: [PATCH for mm] Remove iBCS support, David Newall, (Thu Jan 24, 10:14 pm)
Re: [PATCH for mm] Remove iBCS support, Alan Cox, (Fri Jan 25, 12:40 pm)
Re: [PATCH for mm] Remove iBCS support, Ingo Molnar, (Tue Jan 22, 11:49 am)
Re: [PATCH for mm] Remove iBCS support, David Newall, (Thu Jan 24, 1:01 pm)
Re: [PATCH for mm] Remove iBCS support, Karl Kiniger, (Tue Jan 22, 8:42 am)
Re: [PATCH for mm] Remove iBCS support, Karl Kiniger, (Tue Jan 22, 6:24 am)
Re: [PATCH for mm] Remove iBCS support, Andi Kleen, (Wed Jan 23, 4:48 am)
Re: [PATCH for mm] Remove iBCS support, Karl Kiniger, (Wed Jan 23, 10:12 am)
Re: [PATCH for mm] Remove iBCS support, Andi Kleen, (Wed Jan 23, 10:24 am)
Re: [PATCH for mm] Remove iBCS support, David Newall, (Thu Jan 24, 1:06 pm)
Re: [PATCH for mm] Remove iBCS support, David Newall, (Tue Jan 22, 11:06 am)
Re: [PATCH for mm] Remove iBCS support, Adrian Bunk, (Tue Jan 22, 11:52 am)