lkml.org 
[lkml]   [2015]   [Sep]   [30]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH v2 1/2] x86/msr: Carry on after a non-"safe" MSR access fails without !panic_on_oops

* Peter Zijlstra <peterz@infradead.org> wrote:

> On Mon, Sep 21, 2015 at 09:36:15AM -0700, Linus Torvalds wrote:
> > On Mon, Sep 21, 2015 at 1:46 AM, Ingo Molnar <mingo@kernel.org> wrote:
> > >
> > > Linus, what's your preference?
> >
> > So quite frankly, is there any reason we don't just implement
> > native_read_msr() as just
> >
> > unsigned long long native_read_msr(unsigned int msr)
> > {
> > int err;
> > unsigned long long val;
> >
> > val = native_read_msr_safe(msr, &err);
> > WARN_ON_ONCE(err);
> > return val;
> > }
> >
> > Note: no inline, no nothing. Just put it in arch/x86/lib/msr.c, and be
> > done with it. I don't see the downside.
> >
> > How many msr reads are <i>so</i> critical that the function call
> > overhead would matter? Get rid of the inline version of the _safe()
> > thing too, and put that thing there too.
>
> There are a few in the perf code, and esp. on cores without a stack engine the
> call overhead is noticeable. Also note that the perf MSRs are generally
> optimized MSRs and less slow (we cannot say fast, they're still MSRs) than
> regular MSRs.

These could still be open coded in an inlined fashion, like the scheduler usage.

Thanks,

Ingo


\
 
 \ /
  Last update: 2015-09-30 16:21    [W:0.102 / U:0.372 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site