lkml.org 
[lkml]   [2008]   [Oct]   [23]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH] Skip tsc synchronization checks if CONSTANT_TSC bit is set.
Alok Kataria wrote:
>
> I am ok with the CONSTANT_TSC bit check, but if people think that its
> not important to skip this for native, i think adding a new flag to skip
> this should be safe enough.
>
> Ingo, HPA your views on this whole detection and skipping thing ?
>

Okay, first of all, I'm somewhat leery (to put it mildly) of trusting a
CPUID bit to tell me a *system* property, which is that all cores in the
system are synchronized. The CPU designer will know that all the cores
in the *package* are synchronized, but if that extends system-wide is a
property beyond the CPU. Now, if I'm not completely mistaken, in the
case of AMD this bit is actually set by the BIOS via a magic MSR, but
that doesn't mean it can't be wrong.

As far as skipping the check, it makes sense for me in the case of known
virtualization platforms; a CPU feature bit, real or synthetic, is a
very clean way to do that. In general we should centralize CPU
knowledge to arch/x86/kernel/cpu and have the code outside look for
specific feature flags, and that applies to virtualization platforms, too.

-hpa


\
 
 \ /
  Last update: 2008-10-24 01:51    [W:0.918 / U:0.344 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site