On Mon, 15 Jan 2018, Paul E. McKenney wrote: > On Sun, Jan 14, 2018 at 02:44:15PM -0800, Paul E. McKenney wrote: > > On Sun, Jan 14, 2018 at 02:31:07PM -0800, tip-bot for Thomas Gleixner wrote: > > > Commit-ID: ed4bbf7910b28ce3c691aef28d245585eaabda06 > > > Gitweb: https://git.kernel.org/tip/ed4bbf7910b28ce3c691aef28d245585eaabda06 > > > Author: Thomas Gleixner <tglx@xxxxxxxxxxxxx> > > > AuthorDate: Sun, 14 Jan 2018 23:19:49 +0100 > > > Committer: Thomas Gleixner <tglx@xxxxxxxxxxxxx> > > > CommitDate: Sun, 14 Jan 2018 23:25:33 +0100 > > > > > > timers: Unconditionally check deferrable base > > > > > > When the timer base is checked for expired timers then the deferrable base > > > must be checked as well. This was missed when making the deferrable base > > > independent of base::nohz_active. > > > > Very cool, thank you! I have fired up some of the dreaded TREE01 tests. > > And (tentatively) a change in behavior! That's the least thing I expected. None of this stuff should use deferrable timers. But what do I know. > In one case, I did not see stall warnings (at least not until the ftrace > dump at test end), but just the occasional "Waylayed timer" message: > > [ 1316.628105] schedule_timeout: Waylayed timer base->clk: 0x1000eff23 jiffies: 0x1000f8335 base->next_expiry: 0x1000eff23 timer->flags: 0x3c800006 timer->expires 0x1000f62ca idx: f2 idx_now: 139 base->pending_map 000000080000000000000000000000000000000000000000100400002000000000000000000000000000010000000000000000000000000000000000000000000000000000000000 > [ 1316.638372] Torture onoff task state: > [ 1316.639774] rcu_preempt I14984 8 2 0x80000000 > [ 1316.641766] Call Trace: > [ 1316.642757] ? __schedule+0x33c/0x6f0 > [ 1316.644109] ? trace_event_raw_event_timer_start+0x6d/0xb0 > [ 1316.646042] schedule+0x37/0x90 > [ 1316.647219] schedule_timeout+0x159/0x470 > [ 1316.648825] ? __next_timer_interrupt+0xc0/0xc0 > [ 1316.650459] rcu_gp_kthread+0x9ee/0x1090 > [ 1316.652147] kthread+0xf0/0x130 > [ 1316.653415] ? rcu_oom_notify+0xd0/0xd0 > [ 1316.654790] ? kthread_destroy_worker+0x40/0x40 > [ 1316.656470] ret_from_fork+0x1f/0x30 > > If I am reading the waylay message correctly, the timer was delayed by > about 8.3 seconds instead of the 21 seconds required to cause an RCU > CPU stall warning. I am going to rearrange the ftrace-dump code a bit > and run more tests. Would be interesting to stop the trace right when you detect the waylay. > [ 382.482303] ret_from_fork+0x1f/0x30 > > I don't have enough runs to be sure, but my current (sad) guess is that > the error rate is unchanged. That patch really should not make any difference. We are wading through traces and are still puzzled.... Thanks, tglx -- To unsubscribe from this list: send the line "unsubscribe linux-tip-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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