Re: [PATCH] block: Improve shared tag set performance

[Bart Van Assche <bvanassche@acm.org>]

On 10/19/23 21:41, Christoph Hellwig wrote:
> On Wed, Oct 18, 2023 at 11:00:56AM -0700, Bart Van Assche wrote:
>> Note: it has been attempted to rework this algorithm. See also "[PATCH
>> RFC 0/7] blk-mq: improve tag fair sharing"
>> (https://lore.kernel.org/linux-block/20230618160738.54385-1-yukuai1@huaweicloud.com/).
>> Given the complexity of that patch series, I do not expect that patch
>> series to be merged.
> 
> Work is hard, so let's skip it?  That's not really the most convincing
> argument.  Hey, I'm the biggest advocate for code improvement by code
> removal, but you better have a really good argument why it doesn't hurt
> anyone.

Hi Christoph,

No, it's not because it's hard to improve the tag fairness algorithm
that I'm proposing to skip this work. It's because I'm convinced that
an improved fairness algorithm will have a negative performance impact
that is larger than that of the current algorithm.

Do you agree that the legacy block layer never had any such fairness
algorithm and also that nobody ever complained about fairness issues
for the legacy block layer? I think that's a strong argument in favor of
removing the fairness algorithm.

Thanks,

Bart.