Re: How should anaconda check for PAE? (was Re: arch fun.)
Thorsten Leemhuis wrote: On 25.02.2009 13:27, Chris Lalancette wrote: Gerd Hoffmann wrote: We can also simply do this: - Install PAE kernel if the CPU supports PAE. i.e. make PAE the default kernel. Yes, I really think we should just do this. It's simple, it means we get the logic right for Xen as well as bare-metal (without any special cases), and the performance hit for those who have PAE and 4GB isn't that bad, I don't think (although numbers one way or the other would be interesting to see). What about compatibility problems? My old laptop had a PAE capable CPU but could not boot a PAE kernel -- I noticed when I was trying a PAE kernel for some tests two or three years ago. I asked a kernel-developer back then if it was worth reporting and I got told that such problems are not unusual and often BIOS or hardware problems. Those likely didn't vanish magically is that statement is correct. Hm, it's an interesting point, and not one that I've heard about or seen before. Xen in Fedora required PAE for quite some time, and despite plenty of other problems (mostly having to do with people wanting to run Xen on non-PAE platforms), we didn't hear about any of this specific problem. Doesn't mean it doesn't exist, though :). Do you have pointers to specific problems? A quick google didn't turn up anything, but I didn't try all that hard. -- Chris Lalancette ___ Fedora-kernel-list mailing list Fedora-kernel-list@redhat.com https://www.redhat.com/mailman/listinfo/fedora-kernel-list
Re: How should anaconda check for PAE? (was Re: arch fun.)
On Wed, 25 Feb 2009 14:15:37 +0100 Thorsten Leemhuis fed...@leemhuis.info wrote: On 25.02.2009 13:27, Chris Lalancette wrote: Gerd Hoffmann wrote: We can also simply do this: - Install PAE kernel if the CPU supports PAE. i.e. make PAE the default kernel. Yes, I really think we should just do this. It's simple, it means we get the logic right for Xen as well as bare-metal (without any special cases), and the performance hit for those who have PAE and 4GB isn't that bad, I don't think (although numbers one way or the other would be interesting to see). What about compatibility problems? My old laptop had a PAE capable CPU but could not boot a PAE kernel -- I noticed when I was trying a PAE kernel for some tests two or three years ago. I asked a kernel-developer back then if it was worth reporting and I got told that such problems are not unusual and often BIOS or hardware problems. Those likely didn't vanish magically is that statement is correct. The algorithm I posted should handle that. If you support NX or you have 4GB of memory then it's pretty much impossible for you to have one of those old CPUs. And all SVM/VMX capable machines support NX so we'd always have the right kernel for them too. ___ Fedora-kernel-list mailing list Fedora-kernel-list@redhat.com https://www.redhat.com/mailman/listinfo/fedora-kernel-list
Re: How should anaconda check for PAE? (was Re: arch fun.)
- Should we be using the PAE kernel *regardless* of memory size (as implied above) or do we want some memory requirements? It's always preferable on hardware (where pae actually works) that also has the nx cpu feature. True PROT_EXEC enforcement (NX) is only available in PAE mode. Thanks, Roland ___ Fedora-kernel-list mailing list Fedora-kernel-list@redhat.com https://www.redhat.com/mailman/listinfo/fedora-kernel-list
Re: How should anaconda check for PAE? (was Re: arch fun.)
On Tue, 24 Feb 2009 15:38:42 -0800 (PST) Roland McGrath rol...@redhat.com wrote: If we have NX (which anything made in the last few years will) it's a performance win to use the hardware NX instead of the segment limit hack we implemented in execshield. It's more than performance. The segment limit hack is a hack, and does not actually do full enforcement in all cases (though we have already bent over backward to ensure that these cases do not come up by default). Hardware NX is 100% reliable. We also need to look for lm to see if we can install a 64-bit kernel. So something like: if (lm) install 64-bit else if (!pae) || (!nx memory 4GB) install i586 else install PAE ___ Fedora-kernel-list mailing list Fedora-kernel-list@redhat.com https://www.redhat.com/mailman/listinfo/fedora-kernel-list
