netdev - Re: [PATCH net-next] net: sched: refactor flower walk to iterate over idr

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Date:   Fri, 13 Jul 2018 13:16:56 +0200
From:   Simon Horman <simon.horman@...ronome.com>
To:     Vlad Buslov <vladbu@...lanox.com>
Cc:     netdev@...r.kernel.org, davem@...emloft.net, jhs@...atatu.com,
        xiyou.wangcong@...il.com, jiri@...nulli.us
Subject: Re: [PATCH net-next] net: sched: refactor flower walk to iterate
 over idr

On Tue, Jul 10, 2018 at 08:02:10PM +0300, Vlad Buslov wrote:
> 
> On Tue 10 Jul 2018 at 13:55, Simon Horman <simon.horman@...ronome.com> wrote:
> > On Mon, Jul 09, 2018 at 01:29:11PM +0300, Vlad Buslov wrote:
> >> Extend struct tcf_walker with additional 'cookie' field. It is intended to
> >> be used by classifier walk implementations to continue iteration directly
> >> from particular filter, instead of iterating 'skip' number of times.
> >> 
> >> Change flower walk implementation to save filter handle in 'cookie'. Each
> >> time flower walk is called, it looks up filter with saved handle directly
> >> with idr, instead of iterating over filter linked list 'skip' number of
> >> times. This change improves complexity of dumping flower classifier from
> >> quadratic to linearithmic. (assuming idr lookup has logarithmic complexity)
> >> 
> >> Reviewed-by: Jiri Pirko <jiri@...lanox.com>
> >> Signed-off-by: Vlad Buslov <vladbu@...lanox.com>
> >
> > Reported-by: Simon Horman <simon.horman@...ronome.com>
> >
> > Thanks, I'm very pleased to see this change. I would appreciate it if
> > we could have a little time to test its impact on performance
> > thoroughly.
> 
> For me it reduced time needed to dump 5m flows to ~50 seconds. Not a
> very thorough benchmark, but performance improvement was so dramatic
> that I decided to not investigate further.

Thanks, we have also now measured a similar improvement in performance.

> > One question: will this work as expected (i.e. be at least backwards
> > compatible) with existing user-space code?
> 
> I considered that and didn't find any reason why it would break
> compatibility. Basically with current flower flows are dumped in
> arbitrary order, and with this change dump(accidentally) outputs flows
> in sorted ascending order. User space shouldn't expect any ordering in
> dumped flows anyway, right?

Agreed. I don't think we need to be worried about changes in
the order of dumped flows.

Reviewed-by: Simon Horman <simon.horman@...ronome.com>