From: SeongJae Park <sjpark@amazon.com>
To: "Paul E. McKenney" <paulmck@kernel.org>
Cc: SeongJae Park <sjpark@amazon.com>,
Eric Dumazet <eric.dumazet@gmail.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>
Subject: Re: Re: Re: Re: Re: Re: [PATCH net v2 0/2] Revert the 'socket_alloc' life cycle change
Date: Wed, 6 May 2020 17:20:25 +0200 [thread overview]
Message-ID: <20200506152025.22085-1-sjpark@amazon.com> (raw)
In-Reply-To: <20200506144151.GZ2869@paulmck-ThinkPad-P72> (raw)
On Wed, 6 May 2020 07:41:51 -0700 "Paul E. McKenney" <paulmck@kernel.org> wrote:
> On Wed, May 06, 2020 at 02:59:26PM +0200, SeongJae Park wrote:
> > TL; DR: It was not kernel's fault, but the benchmark program.
> >
> > So, the problem is reproducible using the lebench[1] only. I carefully read
> > it's code again.
> >
> > Before running the problem occurred "poll big" sub test, lebench executes
> > "context switch" sub test. For the test, it sets the cpu affinity[2] and
> > process priority[3] of itself to '0' and '-20', respectively. However, it
> > doesn't restore the values to original value even after the "context switch" is
> > finished. For the reason, "select big" sub test also run binded on CPU 0 and
> > has lowest nice value. Therefore, it can disturb the RCU callback thread for
> > the CPU 0, which processes the deferred deallocations of the sockets, and as a
> > result it triggers the OOM.
> >
> > We confirmed the problem disappears by offloading the RCU callbacks from the
> > CPU 0 using rcu_nocbs=0 boot parameter or simply restoring the affinity and/or
> > priority.
> >
> > Someone _might_ still argue that this is kernel problem because the problem
> > didn't occur on the old kernels prior to the Al's patches. However, setting
> > the affinity and priority was available because the program received the
> > permission. Therefore, it would be reasonable to blame the system
> > administrators rather than the kernel.
> >
> > So, please ignore this patchset, apology for making confuse. If you still has
> > some doubts or need more tests, please let me know.
> >
> > [1] https://github.com/LinuxPerfStudy/LEBench
> > [2] https://github.com/LinuxPerfStudy/LEBench/blob/master/TEST_DIR/OS_Eval.c#L820
> > [3] https://github.com/LinuxPerfStudy/LEBench/blob/master/TEST_DIR/OS_Eval.c#L822
>
> Thank you for chasing this down!
>
> I have had this sort of thing on my list as a potential issue, but given
> that it is now really showing up, it sounds like it is time to bump
> up its priority a bit. Of course there are limits, so if userspace is
> running at any of the real-time priorities, making sufficient CPU time
> available to RCU's kthreads becomes userspace's responsibility. But if
> everything is running at SCHED_OTHER (which is this case here, correct?),
Correct.
> then it is reasonable for RCU to do some work to avoid this situation.
That would be also great!
>
> But still, yes, the immediate job is fixing the benchmark. ;-)
Totally agreed.
>
> Thanx, Paul
>
> PS. Why not just attack all potential issues on my list? Because I
> usually learn quite a bit from seeing the problem actually happen.
> And sometimes other changes in RCU eliminate the potential issue
> before it has a chance to happen.
Sounds interesting, I will try some of those in my spare time ;)
Thanks,
SeongJae Park
next prev parent reply other threads:[~2020-05-06 15:21 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-05 8:10 [PATCH net v2 0/2] Revert the 'socket_alloc' life cycle change SeongJae Park
2020-05-05 8:10 ` [PATCH net v2 1/2] Revert "coallocate socket_wq with socket itself" SeongJae Park
2020-05-06 4:55 ` kbuild test robot
2020-05-05 8:10 ` [PATCH net v2 2/2] Revert "sockfs: switch to ->free_inode()" SeongJae Park
2020-05-05 11:54 ` [PATCH net v2 0/2] Revert the 'socket_alloc' life cycle change SeongJae Park
2020-05-05 12:31 ` Nuernberger, Stefan
2020-05-05 14:53 ` Eric Dumazet
2020-05-05 15:07 ` SeongJae Park
2020-05-05 15:20 ` Eric Dumazet
2020-05-05 15:46 ` SeongJae Park
2020-05-05 16:00 ` Eric Dumazet
2020-05-05 16:13 ` SeongJae Park
2020-05-05 16:25 ` Eric Dumazet
2020-05-05 16:31 ` Eric Dumazet
2020-05-05 16:37 ` Eric Dumazet
2020-05-05 17:05 ` SeongJae Park
2020-05-05 17:30 ` Paul E. McKenney
2020-05-05 17:56 ` SeongJae Park
2020-05-05 18:17 ` Paul E. McKenney
2020-05-05 18:34 ` SeongJae Park
2020-05-05 18:49 ` Paul E. McKenney
2020-05-06 12:59 ` SeongJae Park
2020-05-06 14:33 ` Eric Dumazet
2020-05-06 14:41 ` Paul E. McKenney
2020-05-06 15:20 ` SeongJae Park [this message]
2020-05-05 17:28 ` Paul E. McKenney
2020-05-05 18:11 ` SeongJae Park
2020-05-05 17:23 ` Paul E. McKenney
2020-05-05 17:49 ` SeongJae Park
2020-05-05 18:27 ` Paul E. McKenney
2020-05-05 18:40 ` SeongJae Park
2020-05-05 18:48 ` Paul E. McKenney
2020-05-05 16:26 ` Al Viro
2020-05-05 18:48 ` David Miller
2020-05-05 19:00 ` David Miller
2020-05-06 6:24 ` SeongJae Park
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