From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752842AbdLGQPC (ORCPT ); Thu, 7 Dec 2017 11:15:02 -0500 Received: from mail.kernel.org ([198.145.29.99]:51824 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752819AbdLGQO4 (ORCPT ); Thu, 7 Dec 2017 11:14:56 -0500 DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 0B048219AC Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=frederic@kernel.org X-Google-Smtp-Source: AGs4zMZpYnQMughpYUnvCk0AxpkYLLlNYdSW7vXUiEEKYMTf+pKnkSO6J3FNCMrNBoZ5Y8v+MoTQ6E8UKaR3AvCIVOE= MIME-Version: 1.0 In-Reply-To: <20171204171648.GU7829@linux.vnet.ibm.com> References: <20171130202046.GA27138@linux.vnet.ibm.com> <20171202192419.GN7829@linux.vnet.ibm.com> <20171204171648.GU7829@linux.vnet.ibm.com> From: Frederic Weisbecker Date: Thu, 7 Dec 2017 17:14:54 +0100 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH] sched/isolation: Make NO_HZ_FULL select CPU_ISOLATION To: paulmck@linux.vnet.ibm.com Cc: linux-kernel@vger.kernel.org, xiaolong.ye@intel.com, tglx@linutronix.de, cmetcalf@mellanox.com, cl@linux.com, torvalds@linux-foundation.org, lcapitulino@redhat.com, efault@gmx.de, peterz@infradead.org, riel@redhat.com, kernellwp@gmail.com, mingo@kernel.org, john.stultz@linaro.org Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 2017-12-04 18:16 UTC+01:00, Paul E. McKenney : > On Mon, Dec 04, 2017 at 04:53:15PM +0100, Frederic Weisbecker wrote: >> 2017-12-02 20:24 UTC+01:00, Paul E. McKenney >> I would prefer to keep it. It's useful for automated boot testing >> based on configs such as 0-day or -tip test machines. But I'm likely >> to migrate it to isolcpus implementation. Maybe something along the >> lines of CONFIG_CPU_ISOLATION_ALL. > > How about instead allowing something like "nohz_full=1-" specify that > all CPUs other than CPU 0 should be nohz_full CPUs? That would shrink > the code by eliminating CONFIG_NO_HZ_FULL_ALL while still allowing > easy automation of that particular scenario. > > (Right now, the boot code complains about "nohz_full=1-", which means > that whatever is generating the boot parameters needs to know how many > CPUs there really are, which as you say can be a pain.) Yes but automated boot testing is rather based on configs than boot options. It's much easier. I think that's how Wu Fengguang lab works, and -tip automated tests as well. > >> >> Did you have any nohz_full= or isolcpus= boot options? >> > >> > Replacing CONFIG_NO_HZ_FULL_ALL=y with nohz_full=1-7 works, that >> > is CONFIG_NO_HZ_FULL=y, CONFIG_NO_HZ_FULL_ALL=n, and nohz_full=1-7 >> > on an eight-CPU test. >> > >> > But it is relatively easy to test. Running the rcutorture TREE04 >> > scenario on a four-socket x86 gets me RCU CPU stall warnings within >> > a few minutes more than half the time. ;-) >> >> Indeed I managed to trigger something. If it's the same thing I should >> be able to track down the root cause. >> >> [ 123.907557] ??? Writer stall state RTWS_STUTTER(8) g160 c160 f0x0 >> ->state 0x1 cpu 2 >> [ 123.915184] rcu_torture_wri S 0 111 2 0x80080000 >> [ 123.920673] Call Trace: >> [ 123.923096] ? __schedule+0x2bf/0xbb0 >> [ 123.926715] ? _raw_spin_unlock_irqrestore+0x59/0x70 >> [ 123.931657] schedule+0x3c/0x90 >> [ 123.934777] schedule_timeout+0x1e1/0x560 > > It might well be the same thing, as this schedule_timeout() does look > familiar. I have some diagnostic patches in -rcu, please see below > for the overall effect. I fear I can hit that even without any nohz_full CPU as well. > > Thanx, Paul > >> [ 123.938785] ? __next_timer_interrupt+0xd0/0xd0 >> [ 123.943276] stutter_wait+0xc5/0xe0 >> [ 123.946738] rcu_torture_writer+0x1ae/0x730 >> [ 123.950912] ? rcu_torture_pipe_update+0xf0/0xf0 >> [ 123.955491] kthread+0x15f/0x1a0 >> [ 123.958702] ? kthread_unpark+0x60/0x60 >> [ 123.962523] ret_from_fork+0x24/0x30 >> [ 123.966091] rcu_preempt: wait state: 1 ->state: 0x402 >> [ 123.971112] rcu_sched: wait state: 1 ->state: 0x402 >> [ 123.975953] rcu_bh: wait state: 1 ->state: 0x402 > > ------------------------------------------------------------------------ > > diff --git a/kernel/time/timer.c b/kernel/time/timer.c > index ffebcf878fba..23af27461d8c 100644 > --- a/kernel/time/timer.c > +++ b/kernel/time/timer.c > @@ -1755,8 +1755,13 @@ static void process_timeout(struct timer_list *t) > */ > signed long __sched schedule_timeout(signed long timeout) > { > + struct timer_base *base; > struct process_timer timer; > unsigned long expire; > + unsigned long flags; > + unsigned long i; > + unsigned int idx, idx_now; > + unsigned long j; > > switch (timeout) > { > @@ -1793,6 +1798,17 @@ signed long __sched schedule_timeout(signed long > timeout) > timer_setup_on_stack(&timer.timer, process_timeout, 0); > __mod_timer(&timer.timer, expire, 0); > schedule(); > + j = jiffies; > + if (timeout < 5 && time_after(j, expire + 8 * HZ) && > timer_pending(&timer.timer)) { > + base = lock_timer_base(&timer.timer, &flags); > + idx = timer_get_idx(&timer.timer); > + idx_now = calc_wheel_index(j, base->clk); > + raw_spin_unlock_irqrestore(&base->lock, flags); > + pr_info("%s: Waylayed timer base->clk: %#lx jiffies: %#lx > base->next_expiry: %#lx timer->flags: %#x timer->expires %#lx idx: %x > idx_now: %x base->pending_map ", __func__, base->clk, j, base->next_expiry, > timer.timer.flags, timer.timer.expires, idx, idx_now); > + for (i = 0; i < WHEEL_SIZE / sizeof(base->pending_map[0]) / 8; i++) > + pr_cont("%016lx", base->pending_map[i]); > + pr_cont("\n"); > + } > del_singleshot_timer_sync(&timer.timer); > > /* Remove the timer from the object tracker */ > > Hmm, that message doesn't seem to trigger :-s Thanks.