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From:   SeongJae Park <sjpark@amazon.com>
To:     Eric Dumazet <eric.dumazet@gmail.com>
CC:     SeongJae Park <sjpark@amazon.com>,
        Eric Dumazet <edumazet@google.com>,
        David Miller <davem@davemloft.net>,
        Al Viro <viro@zeniv.linux.org.uk>,
        "Jakub Kicinski" <kuba@kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        <sj38.park@gmail.com>, netdev <netdev@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        SeongJae Park <sjpark@amazon.de>, <snu@amazon.com>,
        <amit@kernel.org>, <stable@vger.kernel.org>,
        Paul McKenney <paulmck@kernel.org>
Subject: Re: Re: [PATCH net v2 0/2] Revert the 'socket_alloc' life cycle change
Date:   Tue, 5 May 2020 19:05:53 +0200
Message-ID: <20200505170553.24056-1-sjpark@amazon.com>
In-Reply-To: <67bdfac9-0d7d-0bbe-dc7a-d73979fd8ed9@gmail.com> (raw)
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On Tue, 5 May 2020 09:37:42 -0700 Eric Dumazet <eric.dumazet@gmail.com> wrote:

> 
> 
> On 5/5/20 9:31 AM, Eric Dumazet wrote:
> > 
> > 
> > On 5/5/20 9:25 AM, Eric Dumazet wrote:
> >>
> >>
> >> On 5/5/20 9:13 AM, SeongJae Park wrote:
> >>> On Tue, 5 May 2020 09:00:44 -0700 Eric Dumazet <edumazet@google.com> wrote:
> >>>
> >>>> On Tue, May 5, 2020 at 8:47 AM SeongJae Park <sjpark@amazon.com> wrote:
> >>>>>
> >>>>> On Tue, 5 May 2020 08:20:50 -0700 Eric Dumazet <eric.dumazet@gmail.com> wrote:
> >>>>>
> >>>>>>
> >>>>>>
> >>>>>> On 5/5/20 8:07 AM, SeongJae Park wrote:
> >>>>>>> On Tue, 5 May 2020 07:53:39 -0700 Eric Dumazet <edumazet@google.com> wrote:
> >>>>>>>
> >>>>>>
[...]
> >>
> >> I would ask Paul opinion on this issue, because we have many objects
> >> being freed after RCU grace periods.
> >>
> >> If RCU subsystem can not keep-up, I guess other workloads will also suffer.
> >>
> >> Sure, we can revert patches there and there trying to work around the issue,
> >> but for objects allocated from process context, we should not have these problems.
> >>
> > 
> > I wonder if simply adjusting rcu_divisor to 6 or 5 would help 
> > 
> > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> > index d9a49cd6065a20936edbda1b334136ab597cde52..fde833bac0f9f81e8536211b4dad6e7575c1219a 100644
> > --- a/kernel/rcu/tree.c
> > +++ b/kernel/rcu/tree.c
> > @@ -427,7 +427,7 @@ module_param(qovld, long, 0444);
> >  static ulong jiffies_till_first_fqs = ULONG_MAX;
> >  static ulong jiffies_till_next_fqs = ULONG_MAX;
> >  static bool rcu_kick_kthreads;
> > -static int rcu_divisor = 7;
> > +static int rcu_divisor = 6;
> >  module_param(rcu_divisor, int, 0644);
> >  
> >  /* Force an exit from rcu_do_batch() after 3 milliseconds. */
> > 
> 
> To be clear, you can adjust the value without building a new kernel.
> 
> echo 6 >/sys/module/rcutree/parameters/rcu_divisor
> 

I tried value 6, 5, and 4, but none of those removed the problem.


Thanks,
SeongJae Park