Re: [PATCH] netfilter: conntrack: use power efficient workqueue

[Pablo Neira Ayuso <pablo@netfilter.org>]

On Mon, Nov 06, 2017 at 04:15:42PM +0100, Vincent Guittot wrote:
> Hi Pablo,
> 
> On 6 November 2017 at 15:56, Pablo Neira Ayuso <pablo@netfilter.org> wrote:
> > On Mon, Nov 06, 2017 at 03:31:55PM +0100, Pablo Neira Ayuso wrote:
> >> On Thu, 2 Nov 2017 15:16:07 +0100 Vincent Guittot <vincent.guittot@linaro.org> wrote:
> >> > conntrack uses the bounded system_long_wq workqueue for its works that
> >> > don't have to run on the cpu they have been queued.  Using bounded
> >> > workqueue prevents the scheduler to make smart decision about the best
> >> > place to schedule the work.
> >> >
> >> > This patch replaces system_long_wq with system_power_efficient_wq.
> >> > the work stays bounded to a cpu by default unless the
> >> > CONFIG_WQ_POWER_EFFICIENT is enable. In the latter case, the work can
> >> > be scheduled on the best cpu from a power or a performance point of
> >> > view.
> >>
> >> Applied, thanks.
> >
> > I'm stepping back. According to what I'm reading
> > system_power_efficient_wq becomes system_wq when disabled, which is
> > not semantically the same as system_long_wq that we have now.
> 
> When disabled, system_power_efficient_wq behaves like system_wq (and
> system_long_wq) as the worqueue are bounded to a cpu but It stays a
> different workqueue.
>
> > My concern is that the conntrack garbage collector may run for quite a
> > bit of time. Did you test this with a large conntrack table full of
> 
> No, I haven't done specific tests with a large conntrack table full of entries.
> 
> There is no system_power_efficient_long_wq. I was not convinced that
> we should create one that's why I have used system_power_efficient_wq

My concern is that this garbage collector may run intensively on busy
conntrack tables to get rid of expired entries, so my question is if
switching from system_long_wq to system_wq is a real issue.

Thanks.