Re: [PATCH v2 1/3] file-posix: add `aio-max-batch` option

[Kevin Wolf]

Am 27.10.2021 um 11:23 hat Stefano Garzarella geschrieben:
> On Wed, Oct 27, 2021 at 06:28:51AM +0200, Markus Armbruster wrote:
> > Stefano Garzarella <sgarzare@redhat.com> writes:
> > 
> > > Commit d7ddd0a161 ("linux-aio: limit the batch size using
> > > `aio-max-batch` parameter") added a way to limit the batch size
> > > of Linux AIO backend for the entire AIO context.
> > > 
> > > The same AIO context can be shared by multiple devices, so
> > > latency-sensitive devices may want to limit the batch size even
> > > more to avoid increasing latency.
> > > 
> > > For this reason we add the `aio-max-batch` option to the file
> > > backend, which will be used by the next commits to limit the size of
> > > batches including requests generated by this device.
> > > 
> > > Suggested-by: Kevin Wolf <kwolf@redhat.com>
> > > Reviewed-by: Kevin Wolf <kwolf@redhat.com>
> > > Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
> > > ---
> > > 
> > > Notes:
> > >     v2:
> > >     - @aio-max-batch documentation rewrite [Stefan, Kevin]
> > > 
> > >  qapi/block-core.json | 7 +++++++
> > >  block/file-posix.c   | 9 +++++++++
> > >  2 files changed, 16 insertions(+)
> > > 
> > > diff --git a/qapi/block-core.json b/qapi/block-core.json
> > > index 6d3217abb6..fef76b0ea2 100644
> > > --- a/qapi/block-core.json
> > > +++ b/qapi/block-core.json
> > > @@ -2896,6 +2896,12 @@
> > >  #              for this device (default: none, forward the commands via 
> > > SG_IO;
> > >  #              since 2.11)
> > >  # @aio: AIO backend (default: threads) (since: 2.8)
> > > +# @aio-max-batch: maximum number of requests to batch together into a 
> > > single
> > > +#                 submission in the AIO backend. The smallest value 
> > > between
> > > +#                 this and the aio-max-batch value of the IOThread 
> > > object is
> > > +#                 chosen.
> > > +#                 0 means that the AIO backend will handle it 
> > > automatically.
> > > +#                 (default: 0, since 6.2)
> > 
> > "(default 0) (since 6.2)" seems to be more common.
> 
> Indeed I wasn't sure, so I followed @drop-cache, the last one added in
> @BlockdevOptionsFile.

Actually, I think your style is more common, both globally and in
block-*:

    $ git grep -i '[,;] since' qapi/ | wc -l
    17
    $ git grep -i '[,;] since' qapi/block* | wc -l
    12

Compared to:

    $ git grep -i ') (since' qapi/ | wc -l
    14
    $ git grep -i ') (since' qapi/block* | wc -l
    7

Also a few instances with "(since: ...; default: ...)", but none in that
order with separate brackets.

So I'd rather merge this version if this is the only comment.

Kevin