Mark Kettenis wrote:
> But maybe the default rdtsc() should include the lfence. And then we
> could have rdtsc_unordered() for this cases that don't care about
> ordering.
Right.
But I don't like the word 'order', because it is too vague. There
are layers of ordering, speculation, asyncronous
> Date: Sun, 21 Jun 2020 16:55:56 +0100
> From: Stuart Henderson
>
> On 2020/06/21 18:46, Paul Irofti wrote:
> >
> >
> > În 21 iunie 2020 16:30:43 EEST, Theo de Raadt a scris:
> > >Paul Irofti wrote:
> > >
> > >> If you change the name to rdtsc_ordered(), OK.
> > >
> > >That is a weaker name.
On Sun, Jun 21, 2020 at 04:55:56PM +0100, Stuart Henderson wrote:
> On 2020/06/21 18:46, Paul Irofti wrote:
> >
> >
> > În 21 iunie 2020 16:30:43 EEST, Theo de Raadt a scris:
> > >Paul Irofti wrote:
> > >
> > >> If you change the name to rdtsc_ordered(), OK.
> > >
> > >That is a weaker name.
>
> From: "Theo de Raadt"
> Date: Sun, 21 Jun 2020 07:30:43 -0600
>
> Paul Irofti wrote:
>
> > If you change the name to rdtsc_ordered(), OK.
>
> That is a weaker name.
>
> Ordered in what way, at what level; ordered against what?
>
> This is using a specific pipeline ordering known as lfence.
On 2020/06/21 18:46, Paul Irofti wrote:
>
>
> În 21 iunie 2020 16:30:43 EEST, Theo de Raadt a scris:
> >Paul Irofti wrote:
> >
> >> If you change the name to rdtsc_ordered(), OK.
> >
> >That is a weaker name.
> >
> >Ordered in what way, at what level; ordered against what?
> >
> >This is using
În 21 iunie 2020 16:30:43 EEST, Theo de Raadt a scris:
>Paul Irofti wrote:
>
>> If you change the name to rdtsc_ordered(), OK.
>
>That is a weaker name.
>
>Ordered in what way, at what level; ordered against what?
>
>This is using a specific pipeline ordering known as lfence.
>So it might as w
Paul Irofti wrote:
> If you change the name to rdtsc_ordered(), OK.
That is a weaker name.
Ordered in what way, at what level; ordered against what?
This is using a specific pipeline ordering known as lfence.
So it might as well say lfence. That is the technical name for
that type of ordering
it definitely got better:
cpu0: TSC skew=0 observed drift=0
cpu0: TSC skew=0 observed drift=0
cpu1: TSC skew=51 observed drift=0
cpu2: TSC skew=68 observed drift=0
cpu3: TSC skew=68 observed drift=0
cpu4: TSC skew=0 observed drift=0
cpu5: TSC skew=0 observed drift=0
cpu6: TSC skew=85 observed drif
On Sat, Jun 20, 2020 at 10:02:19PM +0200, Mark Kettenis wrote:
> RDTSC is not a serializing instruction; to make sure we get the TSC
> value corresponding to the position of RDTSC in te instruction stream
> we need a barrier. Linux uses LFENCE on machines where it is
> available. FreeBSD seems to
RDTSC is not a serializing instruction; to make sure we get the TSC
value corresponding to the position of RDTSC in te instruction stream
we need a barrier. Linux uses LFENCE on machines where it is
available. FreeBSD seems to prefer MFENCE for AMD CPUs but uses
LFENCE for Intel CPUs. For now my
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