Routing benchmarks

[Jacques Fourie]

On Tue, Sep 9, 2008 at 6:14 PM, Mark Tinguely <tinguely at casselton.net> wrote:
>
> (trimmed the thread text)
>
>>  >> Running netserver on the gumstix shows a throughput of 2.4Mbit/s. At
>>  >> the moment I can't get if_bridge to work - will try to figure out what
>>  >> is going on. A bridging benchmark may be more informative.
>
>>  > My experience in working with architectures like this is that cache handling
>>  > can be a significant cost that doesn't always show up on a profile.
>>  >
>>
>>  Thanks for the nice idea - will try something similar. At the moment
>>  I'm also suspecting that cache handling has got a lot to do with the
>>  performance figures that I'm seeing. The PXA255 has a 32KB data and
>>  32KB instruction cache.
>>
>>  Jacques
>
> which version of freebsd are you using - we changed some cache flushing
> routines between FreeBSD 7.x and current. Unless errors were introduced
> or removed, there should not be that large of a change.
>
> As mentioned, the ARM caches are pretty small. The ARM processors before
> version 6, (anything before ARM10) uses virtually indexed / virtually tagged
> caches, so they need to be flushed on context changes.
>
> The version 6 and version 7 ARM processors (ARM10/ARM11) are either virtually
> indexed / physically tagged or physically indexed / physically tagged.
> The PIPT caches don't need to be flushed on context changes and were needed
> for multiple processor support. The pmap code will have to be re-written to
> take advantage of the PIPT caches (put a process value into the MMU and remove
> most flushes).
>
> Also, the pre version 6 ARM processors didn't allow for any spare bits in the
> PTE for OS use. The newer processors have a bit or two, still not enough
> for FreeBSD's needs, so we need to shadow these bits.
>
> Thirdly, we dynamically allocate a seperate structure that mirrors the
> page table. I think I have all the "paper scratching" required to move from
> this structure to the FreeBSD i386/amd64 recursive page table approach.
>
> --Mark Tinguely.
>

I'm using -current from about a week ago.

Jacques