Messages in this thread |  | | | Date | Wed, 13 Aug 2008 17:40:43 +0200 | | From | Ingo Molnar <> | | Subject | Re: pthread_create() slow for many threads; also time to revisit 64b context switch optimization? |
| |
* Ulrich Drepper <drepper@redhat.com> wrote:
> -----BEGIN PGP SIGNED MESSAGE----- > Hash: SHA1 > > Ingo Molnar wrote: > > i find it pretty unacceptable these days that we limit any aspect of > > pure 64-bit apps in any way to 4GB (or any other 32-bit-ish limit). > > Sure, but if we can pin-point the sub-archs for which it is the > problem then a flag to optionally request it is even easier to handle. > You'd simply ignore the flag for anything but the P4 architecture.
i suspect you are talking about option #2 i described. It is the option which will take the most time to trickle down to people.
> I personally have no problem removing the whole thing because I have > no such machine running anymore. But there are people out there who > have.
hm, i think the set of people running on such boxes _and_ then upgrading to a new glibc and expecting everything to be just as fast to the microsecond as before should be miniscule. Those P4 derived 64-bit boxes were astonishingly painful in 64-bit mode - most of that hw is running 32-bit i suspect, because 64-bit on it was really a joke.
Btw., can you see any problems with option #1: simply removing MAP_32BIT from 64-bit stack allocations in glibc unconditionally? It's the fastest to execute and also the most obvious solution. +1 usecs overhead in the 64-bit context-switch path on those old slow boxes wont matter much.
10 _millisecs_ to start a single thread on top-of-the-line hw is quite unaccepable. (and there's little sane we can do in the kernel about allocation overhead when we have an imperfectly filled 4GB box for all allocations)
Ingo
|  |