[lkml]   [2008]   [Oct]   [7]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: [PATCH] [1/3] Provide rdtscll() asm/msr.h for user space
Andi Kleen wrote:
> For simple user space timing it's very useful to be able to do
> #include <asm/msr.h> instead of having to cut'n'paste the necessarily
> macros into all programs. This used to work with older kernels,
> but broke with the paravirt support (I ended up with a bunch of
> test programs that broke because of that). But it's very useful
> to have rdtscll() available somewhere in user space and asm/msr.h
> is a good place to have them.
> Provide simple rdtsc/rdtscl() macros for user space too in asm/msr.h.
> Since they are very simple I don't think they are a burden to maintain.
> The diff looks bigger than it is because I moved a code block
> and diff doesn't handle it very well.

I really don't think this belongs in the kernel. It's not even a case
of "usable by accident" anymore, and hasn't worked for a while, so it's
not a matter of legacy, either.

Mixing fundamentally unrelated kernel and userspace variants of the same
function just makes the aggregation uglier than both.

(Also, most userspace variants I have seen have what the kernel calls
"rdtscll" and calls it "rdtsc".)

I would suggest writing a <sys/tsc.h> header file and submitting to the
glibc people, instead, or perhaps even better, start a libarch/libx86 tree.


 \ /
  Last update: 2008-10-07 23:35    [W:0.094 / U:5.292 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site