Re: [PATCH 2/2] libata: micro-optimize tag allocation

[Tejun Heo <tj@kernel.org>]

On Fri, Jan 16, 2015 at 03:13:08PM -0800, Dan Williams wrote:
> Jens notes, "libata tag allocator sucks. Like seriously sucks, it's
> almost a worst case implementation."  Previously I thought SATA mmio
> latency dominated performance profiles, but as Tejun notes:
> 
>   "Hmmm... one problem with the existing tag allocator in ata is that
>    it's not very efficient which actually shows up in profile when libata
>    is used with a very zippy SSD.  Given that ata needs a different
>    allocation policies anyway maybe the right thing to do is making the
>    existing allocator suck less."
> 
> So replace it with a naive enhancement that also supports the existing
> quirks.  Hopefully, soon to be replaced by Shaohua's patches [1], but
> those do not yet support the quirk needed by sil24 (ATA_FLAG_LOWTAG)
> [2].
> 
> [1]: http://marc.info/?l=linux-ide&m=142137195324687&w=2
> [2]: https://bugzilla.kernel.org/show_bug.cgi?id=87101
> 
> Cc: Jens Axboe <axboe@fb.com>
> Cc: Tejun Heo <tj@kernel.org>
> Cc: Shaohua Li <shli@fb.com>
> Cc: Christoph Hellwig <hch@infradead.org>
> Signed-off-by: Dan Williams <dan.j.williams@intel.com>

Hmmm... if libata using blk-tag isn't ugly, I think that prolly is the
better way to proceed.  Let's see how that develops.

Thanks.

-- 
tejun