Re: [PATCH 2/4] block: inline fast path of driver tag allocation

Christoph Hellwig
2021-10-13T17:58:37Z

On Wed, Oct 13, 2021 at 11:46:04AM -0600, Jens Axboe wrote:
> On 10/13/21 11:22 AM, Christoph Hellwig wrote:
> > On Wed, Oct 13, 2021 at 10:49:35AM -0600, Jens Axboe wrote:
> >> If we don't use an IO scheduler or have shared tags, then we don't need
> >> to call into this external function at all. This saves ~2% for such
> >> a setup.
> >
> > Hmm. What happens if you just throw an inline tag onto
> > blk_mq_get_driver_tag?
>
> I'd be surprised if that's any different than my patch in terms of
> performance, the fast path would be about the same. I don't feel
> strongly about it, can do that instead.

I find the double indirection in your patch a bit confusing. Not a big
deal if it is actually required, but if we can avoid that I'd prefer
not to add the extra indirection.