Re: don't reorder requests passed to ->queue_rqs

[Jens Axboe <axboe@kernel.dk>]

On 11/13/24 9:16 PM, Christoph Hellwig wrote:
> On Wed, Nov 13, 2024 at 01:51:48PM -0700, Jens Axboe wrote:
>> Thanks for testing, but you can't verify any kind of perf change with
>> that kind of setup. I'll be willing to bet that it'll be 1-2% drop at
>> higher rates, which is substantial. But the reordering is a problem, not
>> just for zoned devices, which is why I chose to merge this.
> 
> So I did not see any variation, but I also don't have access to a really
> beefy setup right now.  If there is a degradation it probably is that
> touching rq_next for each request actually has an effect if the list is
> big enough and they aren't cache hot any more.  I can cook up a patch

Exactly.

> that goes back to the scheme currently used upstream in nvme and virtio
> that just cuts of the list at a hctx change instead of moving the
> requests one by one now that the block layer doesn't mess up the order.

I think that would be useful. I can test.

-- 
Jens Axboe