-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 The Thursday 2008-07-10 at 20:28 +0200, Per Jessen wrote:
Carlos E. R. wrote:
The Thursday 2008-07-10 at 12:55 -0400, Patrick Shanahan wrote:
PAE *is* now the "default" kernel for PAE enabled processor. It takes advantages of processor properties not availaboe in the "real" ?default? kernel. It is to your *advantage* to use it.
Not sure of that... page switching is "heavier", more data to make the switch, thus slower. Sure, the noexecute bit is nice, but perfomance?
That both processor and kernel are PAE enabled doesn't mean that PAE will be used, AFAIU. I asked this particular question on the -factory list a couple of months ago too.
There are two different things to consider in PAE kernels. One is the PAE thing for accessing more memory on 32 bit processors. Obviously, if the machine doesn't have that much memory, it is not needed and will probably not be used. The other is the NX bit, the no execute bit, that allows marking memory pages as code or not code: this is an interesting security feature, but being the 63th bit of an entry in the page table, it requires switching to a 64 bit table instead of the normal 32 bit table, and to get this 64 bit table you need PAE. And this, IMO, is unfortunate, IMO. http://en.wikipedia.org/wiki/Nx_bit The NX bit, which stands for No eXecute, is a technology used in CPUs to segregate areas of memory for use by either storage of processor instructions (or code) or for storage of data, a feature normally only found in Harvard architecture processors. However, the NX bit is being increasingly used in conventional von Neumann architecture processors, for security reasons. ... The NX bit specifically refers to bit number 63 (i.e. the most significant bit) of a 64-bit entry in the page table. If this bit is set to 0, then code can be executed from that page; if set to 1, code cannot be executed from that page, and anything residing there is assumed to be data. Also note that it is used only with Physical Address Extension (PAE) page table format, because the x86's original 32-bit page table format obviously has no bit 63. And the larger page size, will, I fear, slow down machines in the lower end of the speed and memory ranges. This has not been explained or counter-explained. - -- Cheers, Carlos E. R. -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.4-svn0 (GNU/Linux) iD8DBQFIdpKOtTMYHG2NR9URAlgFAJ49hx9n4+6LTdPHt+WklvkXwwfDKgCdHciw 14M/cRp4Gex36gdjixKXx7k= =Mq9d -----END PGP SIGNATURE----- -- To unsubscribe, e-mail: opensuse+unsubscribe@opensuse.org For additional commands, e-mail: opensuse+help@opensuse.org