Re: [PATCH] [5/20] x86: Introduce nsec_barrier()

Ingo Molnar
2008-01-03T10:48:19Z

* Andi Kleen <ak@suse.de> wrote:

> nsec_barrier() is a new barrier primitive that stops RDTSC speculation
> to avoid races with timer interrupts on other CPUs.
>
> Add it to all architectures. Except for x86 it is a nop right now. I
> only tested x86, but it's a very simple change.
>
> On x86 it expands either to LFENCE (for Intel CPUs) or MFENCE (for AMD
> CPUs) which stops RDTSC on all currently known microarchitectures that
> implement SSE. On CPUs without SSE there is generally no RDTSC
> speculation.

i've picked up your rdtsc patches into x86.git but have simplified it:
there's no nsec_barrier() anymore - rdtsc() is always synchronous.
MFENCE/LFENCE is fast enough. Open-coding such barriers almost always
leads to needless trouble. Please check the next x86.git tree.

Ingo