Re: [PATCH 00/14] Initial BPF-JIT support for MIPS

[Markos Chandras <Markos.Chandras@imgtec.com>]

Hi Florian,

On 04/08/2014 07:38 PM, Florian Fainelli wrote:
> Hi,
>
> 2014-04-08 4:47 GMT-07:00 Markos Chandras <markos.chandras@imgtec.com>:
>> Hi,
>>
>> This adds support for BPF-JIT for MIPS. Tested on mips32 LE/BE and mips64 BE
>> with a few networking tools such as tcpdump and dhcp but not all opcodes have
>> been tested as far as I can tell. There are a few optimizations left to be made
>> (fastpath for load operations instead of calling the helper functions) but
>> these can be added later on. If someone has complex network setups in place and
>> would like to give it a try, that would be much appreciated.
>>
>> This patchset is for the upstream-sfr/mips-for-linux-next tree
>
> You should have probably CC'd netdev@vger.kernel.org to get their
> review on the specific JIT implementation.
>
> BPF_JIT is made conditional to MIPS32/64R2 processors, I could not
> spot easily in the implementation whether this is because you are
> using r2-only instructions, or this is just the targets you tested. Is
> there any chance to make that work on MIPS32r1 CPUs for instance?
> Those are used in low-end devices which could benefit from such a
> performance boost.
>
> Thanks!
>
>>

I used in fact only R2 devices. I also use R2 specific instructions such 
as "ins" and "wsbh". I haven't really considered supporting older ISAs 
for a couple of reasons. R2 has been around for a long time so a ~7y old 
device is probably R2 capable. Furthermore, I was not sure whether 
mips32/64R1 devices are likely to run the latest kernel (and/or use 
BPF-JIT at all). But I could easily be wrong.
Having said that, it's possible to support R1 devices but I'd like to 
avoid the overhead so a few #ifdefs are needed in the code. My personal 
preference is to support R2 in the initial patch, and add R1 support 
later on (along with the optimizations I have in mind).

-- 
markos