Port-mips archive
[
Date Prev][
Date Next][
Thread Prev][
Thread Next][
Date Index][
Thread Index][
Old Index]
Re: SGI MIPS, Speculative Execution issue
On 2024年10月27日, DiTBho Down in The Bunny hole wrote:
> > In a cache-coherent system this is resolved transparently by hardware and
> > such synchronisation happens automatically.
>
> Thanks for the clarification =)
You are welcome.
> I wonder why the linux kernel perfectly runs on an O2/R5K, while it
> crashes in less than 10 seconds from boot on an O2/R10K?
I think MIPS/Linux matters will best be discussed at
<linux-mips%vger.kernel.org@localhost>. There are people there who have experience
with running Linux on SGI hardware there (I don't).
> If we assume that it is the CPU that does not implement any
> cache-coherency mechanism, then why does Linux kernel run perfectly on
> an Octane/R10K?
A hardware workaround may have been implemented in a later system, or a
later stepping of the CPU may have the erratum fixed. Also the crash may
be unrelated. You may have to debug it yourself.
> Do NetBSD and OpenBSD work on O2/R10K?
I'll leave answers to this question to the others; I don't know.
> I think (my speculation) the hw-mechanism, it implemented, is external
> to the CPU, but there is more that is not yet clear to me.
In the R4k and R10k architecture coherency logic is on-chip of all the
participating agents, both CPU(s) and DMA masters. See the diagrams in
the respective processor manuals for an overview.
> The post(1) on the mailing list talks about a problem specifically
> related to the speculatively execution of loads and stores on a
> superscalar MIPS4 CPU { R10K, R12K, R14K, R16K }.
There is a section on this erratum in the R10k manual, section 1.7, pp.
21-25. I suggest that you read it, it may help debugging the problem.
> R5K belongs to the MIPS3 class, and it's not superscalar.
The R5k is actually a MIPS IV CPU. And it's dual-issue (between CPU and
FPU instructions). It doesn't implement speculative execution or coherent
operation though.
Maciej
Home |
Main Index |
Thread Index |
Old Index