Re: [PATCH 0/2] Introduce non circular SQ

[Pavel Begunkov <asml.silence@gmail.com>]

On 10/14/25 16:05, Jens Axboe wrote:
> On 10/14/25 4:58 AM, Pavel Begunkov wrote:
>> Add a feature that makes the kernel to ignore SQ head/tail and
>> always start fetching SQ entries from index 0, which helps to
>> keep caches hot. See Patch 2 for more details.
>>
>> liburing support:
>> https://github.com/isilence/liburing.git sq-rewind
>>
>> Tested by forcing liburing to enable the flag for compatible setups.
>>
>> Pavel Begunkov (2):
>>    io_uring: check for user passing 0 nr_submit
>>    io_uring: introduce non-circular SQ
>>
>>   include/uapi/linux/io_uring.h |  6 ++++++
>>   io_uring/io_uring.c           | 34 +++++++++++++++++++++++++---------
>>   io_uring/io_uring.h           |  3 ++-
>>   3 files changed, 33 insertions(+), 10 deletions(-)
> 
> I like the concept of this, makes a lot of sense. No need to keep
> churning through the entire SQ ring, when apps mostly submit a few
> requests at the time. Will help cut down on cacheline usage.
> 
> Curious, do you have any numbers on this for any kind of workload?

No, very likely it's a micro optimisation in the grand picture and
would be hard to measure for anything sensible / realistic. It
shouldn't be too difficult to come up with a test with a bunch of
pinned tasks putting a memory pressure, but that would be as useful
as it sounds.

-- 
Pavel Begunkov