netdev - Re: [PATCH net-next 00/13] Control action percpu counters allocation by netlink flag

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Date:   Thu, 24 Oct 2019 08:12:46 -0700
From:   Roopa Prabhu <roopa@...ulusnetworks.com>
To:     Marcelo Ricardo Leitner <mleitner@...hat.com>
Cc:     Vlad Buslov <vladbu@...lanox.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "jhs@...atatu.com" <jhs@...atatu.com>,
        "xiyou.wangcong@...il.com" <xiyou.wangcong@...il.com>,
        "jiri@...nulli.us" <jiri@...nulli.us>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "dcaratti@...hat.com" <dcaratti@...hat.com>
Subject: Re: [PATCH net-next 00/13] Control action percpu counters allocation
 by netlink flag

On Tue, Oct 22, 2019 at 10:10 AM Marcelo Ricardo Leitner
<mleitner@...hat.com> wrote:
>
> On Tue, Oct 22, 2019 at 03:52:31PM +0000, Vlad Buslov wrote:
> >
> > On Tue 22 Oct 2019 at 18:15, Marcelo Ricardo Leitner <mleitner@...hat.com> wrote:
> > > On Tue, Oct 22, 2019 at 05:17:51PM +0300, Vlad Buslov wrote:
> > >> - Extend actions that are used for hardware offloads with optional
> > >>   netlink 32bit flags field. Add TCA_ACT_FLAGS_FAST_INIT action flag and
> > >>   update affected actions to not allocate percpu counters when the flag
> > >>   is set.
> > >
> > > I just went over all the patches and they mostly make sense to me. So
> > > far the only point I'm uncertain of is the naming of the flag,
> > > "fast_init".  That is not clear on what it does and can be overloaded
> > > with other stuff later and we probably don't want that.
> >
> > I intentionally named it like that because I do want to overload it with
> > other stuff in future, instead of adding new flag value for every single
> > small optimization we might come up with :)
>
> Hah :-)
>
> >
> > Also, I didn't want to hardcode implementation details into UAPI that we
> > will have to maintain for long time after percpu allocator in kernel is
> > potentially replaced with something new and better (like idr is being
> > replaced with xarray now, for example)
>
> I see. OTOH, this also means that the UAPI here would be unstable
> (different meanings over time for the same call), and hopefully new
> behaviors would always be backwards compatible.

+1, I also think optimization flags should be specific to what they optimize.
TCA_ACT_FLAGS_NO_PERCPU_STATS seems like a better choice. It allows
user to explicitly request for it.