Re: [PATCH 0/8] Add support for vectored registered buffers

[Stefan Metzmacher <metze@samba.org>]

Hi Pavel,

>> Add registered buffer support for vectored io_uring operations. That
>> allows to pass an iovec, all entries of which must belong to and
>> point into the same registered buffer specified by sqe->buf_index.
>>
>> The series covers zerocopy sendmsg and reads / writes. Reads and
>> writes are implemented as new opcodes, while zerocopy sendmsg
>> reuses IORING_RECVSEND_FIXED_BUF for the api.
>>
>> Results are aligned to what one would expect from registered buffers:
>>
>> t/io_uring + nullblk, single segment 16K:
>>    34 -> 46 GiB/s
>> examples/send-zerocopy.c default send size (64KB):
>>    82558 -> 123855 MB/s
> 
> Thanks for implementing this, it's great to be able to combine these 2
> optimizations! Though I suspect many applications will want to perform
> vectorized I/O using iovecs that come from different registered
> buffers (e.g. separate header and data allocations). Perhaps a future
> improvement could allow a list of buffer indices to be specified.

I'm wondering about the same. And it's not completely
clear to me what the value of iov_base is in this case,
is it the offset into the buffer, or the real pointer address
that must within the range of the registered buffer?

It might also be very useful to have some vector elements pointing
into one of the registered buffer, while others refer to non-registered
buffers.

metze