Re: memory access op ideas

[Jens Axboe <axboe@kernel.dk>]

On 4/23/22 12:02 PM, Jens Axboe wrote:
> On 4/23/22 11:32 AM, Jens Axboe wrote:
>>> I guess copy_to_user saves us from having to consider endianness.
>>
>> I was considering that too, definitely something that should be
>> investigated. Making it a 1/2/4/8 switch and using put_user() is
>> probably a better idea. Easy enough to benchmark.
> 
> FWIW, this is the current version. Some quick benchmarking doesn't show
> any difference between copy_to_user and put_user, but that may depend on
> the arch as well (using aarch64). But we might as well use put user and
> combine it with the length check, so we explicitly only support 1/2/4/8
> sizes.

In terms of performance, on this laptop, I can do about 36-37M NOP
requests per second. If I use IORING_OP_MEMCPY with immediate mode, it's
around 15M ops/sec. This is regardless of the size, get about the same
whether it's 1 or 8 byte memory writes.

-- 
Jens Axboe