Re: [PATCH v2] fuse: use splice for reading user pages on servers that enable it

[Joanne Koong <joannelkoong@gmail.com>]

On Wed, May 7, 2025 at 7:45 AM Miklos Szeredi <miklos@szeredi.hu> wrote:
>
> On Wed, 23 Apr 2025 at 01:56, Joanne Koong <joannelkoong@gmail.com> wrote:
>
> > For servers that do not need to access pages after answering the
> > request, splice gives a non-trivial improvement in performance.
> > Benchmarks show roughly a 40% speedup.
>
> Hmm, have you looked at where this speedup comes from?
>
> Is this a real zero-copy scenario where the server just forwards the
> pages to a driver which does DMA, so that the CPU never actually
> touches the page contents?

I ran the benchmarks last month on the passthrough_ll server (from the
libfuse examples) with the actual copying out / buffer processing
removed (eg the .write_buf handler immediately returns
"fuse_reply_write(req, fuse_buf_size(in_buf));".

Thanks,
Joanne

>
> Thanks,
> Miklos