Re: [RFC PATCH 00/16] btrfs: offload compression to hardware accelerators

[Christoph Hellwig <hch@infradead.org>]

On Tue, Dec 02, 2025 at 05:46:29PM +0200, Jani Partanen wrote:
> 
> On 02/12/2025 9.53, Christoph Hellwig wrote:
> > On Fri, Nov 28, 2025 at 07:04:48PM +0000, Giovanni Cabiddu wrote:
> > > +---------------------------+---------+---------+---------+---------+
> > > |                           | QAT-L9  | ZSTD-L3 | ZLIB-L3 | LZO-L1  |
> > > +---------------------------+---------+---------+---------+---------+
> > > | Disk Write TPUT (GiB/s)   | 6.5     | 5.2     | 2.2     | 6.5     |
> > > +---------------------------+---------+---------+---------+---------+
> > > | CPU utils %age @208 cores | 4.56%   | 15.67%  | 12.79%  | 19.85%  |
> > > +---------------------------+---------+---------+---------+---------+
> > > | Compression Ratio         | 34%     | 35%     | 37%     | 58%     |
> > > +---------------------------+---------+---------+---------+---------+
> > Is it just me, or do the numbers not look all that great at least
> > when comparing to ZSTD-L3 and LZO-L1?  What are the decompression
> > numbers?
> > 
> 
> What makes you think so?

Well, if you compared QAT-L9 to LZO-L1 specifically:

 - yes, cpu usage is reduced to a quarter
 - disk performance is the same
 - the compression ratio is much, much worse

and we don't know anything about the decompression speed.

All the while you significantly complicate the code.