Re: [Qemu-devel] Poking a sun4v machine

["Andreas Färber" <afaerber@suse.de>]

Am 06.05.2012 10:58, schrieb Alexander Graf:
> Am 06.05.2012 um 10:29 schrieb Blue Swirl <blauwirbel@gmail.com>:
>> On Wed, May 2, 2012 at 2:38 PM, Artyom Tarasenko <atar4qemu@gmail.com> wrote:
>>> On Tue, May 1, 2012 at 4:06 PM, Blue Swirl <blauwirbel@gmail.com> wrote:
>>>> On Tue, May 1, 2012 at 13:54, Artyom Tarasenko <atar4qemu@gmail.com> wrote:
>>>>> To me it looks like at the end do_interrupt will have less
>>>>> common parts between sun4u and sun4v than specific ones.
>>>>
>>>> Same as tlb_fill(), switch() or function pointer. The functions are different.
>>>>
>>>> This is unavoidable (unless maybe in the future the TLB handling can
>>>> be pushed partially higher so mmu_idx parameters can be eliminated)
>>>> and the performance cost is not great.
[...]
>> Architectures are not meant to handle small issues like this.
>> Should performance become a problem, there are a plenty of lower
>> hanging fruits where to start optimizing.
>>
>> Even in this case, rather than the new architecture solution, it could
>> be possible to build separate TLB handlers which call directly the
>> correct MMU functions without switches and these would be selected at
>> translation time or earlier. For the PPCEMB case, maybe the memory API
>> could be changed to handle different page sizes without loss of
>> performance, I don't know. Devices should not depend on
>> TARGET_PAGE_SIZE.
> 
> It's not a matter of an API. The main problem is that the QEMU TLB has to be fine grained enough to handle 1k faults, so it has to be in 1k-steps in its current design.

Due to the TLB being a common property of CPUs yet dependent on target
sizes, I had the idea of breaking it out from CPU(Arch)State so that we
can have a different inheritance hierarchy than for CPUs. But that's
just an unevaluated idea so far and more than 138 commits in the future.

Same problem for breakpoints and watchpoints btw.

ppcemb is no priority for me, but in order to move the very basic halted
and interrupt_request fields to CPUState, for a VMState post_load hook
we need to be able to tlb_flush() based on CPUState rather than
CPUArchState. Currently just a pointer hack on qom-cpu branch; as an
interim solution I might just defer that to target code to workaround
the problem...

Andreas

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