Bryan J. Smith <b.j.smith@ieee.org>
2005-Jun-28 20:51 UTC
[CentOS] [OT] Memory Models and Multi/Virtual-Cores -- WAS: 4.0-> 4.1 update failing
From: Robert Hanson <roberth at abbacomm.net>> or should i be more specific with the question(s)? > the reason i ask is that i just dumped 2 gig dram in a basic > P4 Intel 3.0GHz box to play with. > regards and TIA,At more than 1GiB on Linux/x86, you must use a 4G+4G kernel (this is the default) to see more than 960MiB. This causes a signficant (10%+) performance hit. On more than 4GiB, it is worsened as more extensive paging is used. If you have 1GiB or less, you should rebuild with_out_ "HIGHMEM" support which is a 1G+3G kernel, and you'll see better performance (and memory will be limited to 960MiB). In a nutshell, you should be running Linux/x86-64 on systems with more than 1GiB for optimal performance. If you have more than 4GiB of combined system and memory mapped I/O, you should be running Opterons with I/O MMUs. Intel EM64T systems will have protections in place for both earlier generation GTL+ limitations, as well as lack of an I/O MMU. Much of the additional "tangent" surrounded the fact that there are a few so-called "32-bit" Athlons that actually have a BIOS hack and Linux kernel support so it doesn't take a performance hit. Long story short, it has to do with the fact that even so-called "32-bit" Athlons have a core and underlying interconnect platform that supports 40-bit _linear_ addressing _natively_. -- Bryan J. Smith mailto:b.j.smith at ieee.org
Feizhou
2005-Jun-29 04:20 UTC
[CentOS] [OT] Memory Models and Multi/Virtual-Cores -- WAS: 4.0-> 4.1 update failing
Bryan J. Smith <b.j.smith at ieee.org> wrote:> From: Robert Hanson <roberth at abbacomm.net> > >>or should i be more specific with the question(s)? >>the reason i ask is that i just dumped 2 gig dram in a basic >>P4 Intel 3.0GHz box to play with. >>regards and TIA, > > > At more than 1GiB on Linux/x86, you must use a 4G+4G kernel > (this is the default) to see more than 960MiB. This causes a > signficant (10%+) performance hit. On more than 4GiB, it is > worsened as more extensive paging is used. > > If you have 1GiB or less, you should rebuild with_out_ "HIGHMEM" > support which is a 1G+3G kernel, and you'll see better performance > (and memory will be limited to 960MiB). >I thought they have done away with the high memory bounce buffers? Can you explain what Andi means by this? ----quote---- Current X86-64 implementations only support 40 bit of address space, but we support upto 46bits. This expands into MBZ space in the page tables. -Andi Kleen, Jul 2004 ----quote---- Does it mean that we don't need no fancy tweaks to get direct addressing for over 1G or over 4G? Is that hack for Athlons limited/useful only to Athlon MP boards with the Linux option in BIOS or do Opterons also need that?
Maybe Matching Threads
- [OT] Memory Models and Multi/Virtual-Cores -- WAS: 4.0 -> 4.1 update failing
- Re: [which kernel for AMD Sempron processor?
- Fwd: xe CLI: Error code: MEMORY_CONSTRAINT_VIOLATION - trial XenServer 6.0.2 image has a bug
- Offtopic Posts [was Re: [OT] Memory Models and Multi/Virtual-Cores -- WAS: 4.0 -> 4.1 update failing]
- What have I done wrong?