[GRLUG] Why aren't fast system call instructions being used on my system?

[Matthew Grochowalski]

Figured it out: sep is disabled when NX-bit emulation is enabled. And
NX-bit emulation is enabled by default on all non-PAE Ubuntu kernels.
Supposedly 10.04 and greater Ubuntu installers will download and
install a PAE kernel if you have >3GB of RAM and are connected to the
internet during install. Otherwise the default kernel has PAE disabled
for greater compatibility.

On Fri, Mar 11, 2011 at 2:40 AM, Jeff DeFouw <jeffd at i2k.com> wrote:
> On Thu, Mar 10, 2011 at 05:20:20PM -0500, Matthew Grochowalski wrote:
>> Supposedly the sysenter/sysexit instructions are significantly faster
>> than the traditional 'int $0x80' method of calling a syscall. However,
>> it appears 'int $0x80' is being used on my Pentium 4.
>> I am not seeing 'sep' as one of the flags in /proc/cpuinfo. (sep
>> indicates the process supports the sysenter/sysexit instructions).
>> I am also seeing 'int $0x80' from disassembling linux-gate.dso.1
>
> Not seeing 'sep' is the problem.  The 'sep' in /proc/cpuinfo comes from
> the same information the kernel uses to dynamically set up
> "linux-gate.dso.1".  I see it on my old Pentium III-M laptop with 2.6.26
> (Debian 686 kernel).  Something is disabling it on your system.
>
> --
> Jeff DeFouw <jeffd at i2k.com>
>
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