Re: [PATCHSET 0/5] User mapped provided buffer rings

Jens Axboe
2023-03-15T20:11:30Z

On 3/15/23 2:03?PM, Helge Deller wrote:
> Hi Jens,
>
> Thanks for doing those fixes!
>
> On 3/14/23 18:16, Jens Axboe wrote:
>> One issue that became apparent when running io_uring code on parisc is
>> that for data shared between the application and the kernel, we must
>> ensure that it's placed correctly to avoid aliasing issues that render
>> it useless.
>>
>> The first patch in this series is from Helge, and ensures that the
>> SQ/CQ rings are mapped appropriately. This makes io_uring actually work
>> there.
>>
>> Patches 2..4 are prep patches for patch 5, which adds a variant of
>> ring mapped provided buffers that have the kernel allocate the memory
>> for them and the application mmap() it. This brings these mapped
>> buffers in line with how the SQ/CQ rings are managed too.
>>
>> I'm not fully sure if this ONLY impacts archs that set SHM_COLOUR,
>> of which there is only parisc, or if SHMLBA setting archs (of which
>> there are others) are impact to any degree as well...
>
> It would be interesting to find out. I'd assume that other arches,
> e.g. sparc, might have similiar issues.
> Have you tested your patches on other arches as well?

I don't have any sparc boxes, unfortunately.. But yes, would be
interesting to test on sparc for sure.

I do all my testing on aarch64 and x86-64, and I know that powerpc/s390
has been tested too. But in terms of coverage and regular testing, it's
just the former two.

--
Jens Axboe