Messages in this thread Patch in this message | | | Date | Fri, 15 Aug 2008 19:19:13 +0200 | From | Ingo Molnar <> | Subject | Re: pthread_create() slow for many threads; also time to revisit 64b context switch optimization? |
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* Ulrich Drepper <drepper@gmail.com> wrote:
> -----BEGIN PGP SIGNED MESSAGE----- > Hash: SHA1 > > Jamie Lokier wrote: > > Suggest: > > > > +#define MAP_STACK 0x20000 /* 31bit or 64bit address for stack, */ > > + /* whichever is faster on this CPU */ > > I agree. Except for the comment. > > > > Also, is this _only_ useful for thread stacks, or are there other > > memory allocations where 31-bitness affects execution speed on old P4s? > > Actually, I would define the flag as "do whatever is best assuming the > allocation is used for stacks". > > For instance, minimally the /proc/*/maps output could show "[user > stack]" or something like this. For security, perhaps, setting of > PROC_EXEC can be prevented.
makes sense. Updated patch below. I've also added your Acked-by. Queued it up in tip/x86/urgent, for v2.6.27 merging.
( also, just to make sure: all Linux kernel versions will ignore such extra flags, so you can just update glibc to use this flag unconditionally, correct? )
Ingo
---------------------------> From 2fdc86901d2ab30a12402b46238951d2a7891590 Mon Sep 17 00:00:00 2001 From: Ingo Molnar <mingo@elte.hu> Date: Wed, 13 Aug 2008 18:02:18 +0200 Subject: [PATCH] x86: add MAP_STACK mmap flag
as per this discussion:
http://lkml.org/lkml/2008/8/12/423
Pardo reported that 64-bit threaded apps, if their stacks exceed the combined size of ~4GB, slow down drastically in pthread_create() - because glibc uses MAP_32BIT to allocate the stacks. The use of MAP_32BIT is a legacy hack - to speed up context switching on certain early model 64-bit P4 CPUs.
So introduce a new flag to be used by glibc instead, to not constrain 64-bit apps like this.
glibc can switch to this new flag straight away - it will be ignored by the kernel. If those old CPUs ever matter to anyone, support for it can be implemented.
Signed-off-by: Ingo Molnar <mingo@elte.hu> Acked-by: Ulrich Drepper <drepper@gmail.com> --- include/asm-x86/mman.h | 1 + 1 files changed, 1 insertions(+), 0 deletions(-)
diff --git a/include/asm-x86/mman.h b/include/asm-x86/mman.h index c1682b5..90bc410 100644 --- a/include/asm-x86/mman.h +++ b/include/asm-x86/mman.h @@ -12,6 +12,7 @@ #define MAP_NORESERVE 0x4000 /* don't check for reservations */ #define MAP_POPULATE 0x8000 /* populate (prefault) pagetables */ #define MAP_NONBLOCK 0x10000 /* do not block on IO */ +#define MAP_STACK 0x20000 /* give out an address that is best suited for process/thread stacks */ #define MCL_CURRENT 1 /* lock all current mappings */ #define MCL_FUTURE 2 /* lock all future mappings */
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