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Message-ID: <CAOtvUMf0Zp9C-jT=ymEo6oyxnsgkvSiGDUs5V_56v4Ai2QyBJQ@mail.gmail.com> Date: Tue, 27 Mar 2012 17:02:34 +0200 From: Gilad Ben-Yossef <gilad@...yossef.com> To: Frederic Weisbecker <fweisbec@...il.com> Cc: LKML <linux-kernel@...r.kernel.org>, linaro-sched-sig@...ts.linaro.org, Alessio Igor Bogani <abogani@...nel.org>, Andrew Morton <akpm@...ux-foundation.org>, Avi Kivity <avi@...hat.com>, Chris Metcalf <cmetcalf@...era.com>, Christoph Lameter <cl@...ux.com>, Daniel Lezcano <daniel.lezcano@...aro.org>, Geoff Levand <geoff@...radead.org>, Ingo Molnar <mingo@...nel.org>, Max Krasnyansky <maxk@...lcomm.com>, "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>, Peter Zijlstra <peterz@...radead.org>, Stephen Hemminger <shemminger@...tta.com>, Steven Rostedt <rostedt@...dmis.org>, Sven-Thorsten Dietrich <thebigcorporation@...il.com>, Thomas Gleixner <tglx@...utronix.de>, Zen Lin <zen@...nhuawei.org> Subject: Re: [RFC][PATCH 00/32] Nohz cpusets v2 (adaptive tickless kernel) On Wed, Mar 21, 2012 at 3:58 PM, Frederic Weisbecker <fweisbec@...il.com> wrote: > Hi all, > > A summary of what this is about can be found here: > https://lkml.org/lkml/2011/8/15/245 > > There are still a lot of things to handle. Especially about > what is done by scheduler_tick() but we also need to: > > - completely handle cputime accounting (need to find every "reader" > of cputime and flush cputimes for all of them). > -handle perf > - handle irqtime finegrained accounting > - handle ilb load balancing > - etc... > I gave the new version a spin (x86 8 way VM) and it looks cool. I did get the following warning once, but couldn't recreate it: [ 31.812741] ------------[ cut here ]------------ [ 31.812741] WARNING: at /home/giladb/Workspace/linux/kernel/time/tick-sched.c:706 tick_nohz_account_ticks+0x7c/0x90() [ 31.812741] Hardware name: Bochs [ 31.812741] Modules linked in: [ 31.812741] Pid: 1006, comm: sh Not tainted 3.3.0-rc7+ #167 [ 31.812741] Call Trace: [ 31.812741] [<c102a3ad>] warn_slowpath_common+0x6d/0xa0 [ 31.812741] [<c106be0c>] ? tick_nohz_account_ticks+0x7c/0x90 [ 31.812741] [<c106be0c>] ? tick_nohz_account_ticks+0x7c/0x90 [ 31.812741] [<c102a3fd>] warn_slowpath_null+0x1d/0x20 [ 31.812741] [<c106be0c>] tick_nohz_account_ticks+0x7c/0x90 [ 31.812741] [<c106be5f>] tick_nohz_flush_current_times+0x3f/0x80 [ 31.812741] [<c106bf8d>] tick_nohz_restart_adaptive+0xd/0x30 [ 31.812741] [<c106c02e>] tick_nohz_check_adaptive+0x3e/0x50 [ 31.812741] [<c1018180>] smp_cpuset_update_nohz_interrupt+0x20/0x30 [ 31.812741] [<c1639c6a>] cpuset_update_nohz_interrupt+0x2a/0x30 [ 31.812741] [<c16395fd>] ? _raw_spin_unlock_irq+0xd/0x30 [ 31.812741] [<c10575c6>] finish_task_switch+0x46/0xa0 [ 31.812741] [<c1638558>] __schedule+0x398/0x910 [ 31.812741] [<c10ef2f1>] ? deactivate_slab+0x611/0x730 [ 31.812741] [<c1120777>] ? __find_get_block+0x97/0x1a0 [ 31.812741] [<c1221214>] ? cpumask_next_and+0x24/0xa0 [ 31.812741] [<c10558cb>] ? get_parent_ip+0xb/0x40 [ 31.812741] [<c1638b50>] schedule+0x30/0x50 [ 31.812741] [<c16379b5>] schedule_hrtimeout_range_clock+0xf5/0x110 [ 31.812741] [<c10558cb>] ? get_parent_ip+0xb/0x40 [ 31.812741] [<c10586db>] ? sub_preempt_count+0x7b/0xb0 [ 31.812741] [<c1639633>] ? _raw_spin_unlock_irqrestore+0x13/0x40 [ 31.812741] [<c1054140>] ? __wake_up+0x40/0x50 [ 31.812741] [<c1294d1f>] ? put_ldisc+0x3f/0xa0 [ 31.812741] [<c16379e2>] schedule_hrtimeout_range+0x12/0x20 [ 31.812741] [<c1107969>] poll_schedule_timeout+0x39/0x60 [ 31.812741] [<c1108020>] do_sys_poll+0x400/0x490 [ 31.812741] [<c1054d15>] ? cpuacct_charge+0x65/0x70 [ 31.812741] [<c1107a20>] ? poll_freewait+0x70/0x70 [ 31.812741] [<c1107af0>] ? __pollwait+0xd0/0xd0 [ 31.812741] [<c1107af0>] ? __pollwait+0xd0/0xd0 [ 31.812741] [<c10094a3>] ? native_sched_clock+0x33/0xe0 [ 31.812741] [<c105a0e2>] ? sched_clock_local+0xb2/0x190 [ 31.812741] [<c1054d15>] ? cpuacct_charge+0x65/0x70 [ 31.812741] [<c105b376>] ? update_curr+0x1a6/0x2a0 [ 31.812741] [<c105a2f9>] ? sched_clock_cpu+0x139/0x190 [ 31.812741] [<c105a0e2>] ? sched_clock_local+0xb2/0x190 [ 31.812741] [<c104dd43>] ? hrtimer_forward+0x163/0x1b0 [ 31.812741] [<c10644e2>] ? ktime_get+0x62/0x100 [ 31.812741] [<c1018b56>] ? lapic_next_event+0x16/0x20 [ 31.812741] [<c1069df2>] ? clockevents_program_event+0xc2/0x170 [ 31.812741] [<c106b514>] ? tick_program_event+0x24/0x30 [ 31.812741] [<c104cd1d>] ? hrtimer_interrupt+0x1ad/0x2e0 [ 31.812741] [<c1095128>] ? rcu_pending+0x58/0x70 [ 31.812741] [<c1030a3d>] ? irq_exit+0x6d/0x80 [ 31.812741] [<c1019363>] ? smp_apic_timer_interrupt+0x53/0x90 [ 31.812741] [<c11e0128>] ? avc_has_perm_noaudit+0xc8/0x360 [ 31.812741] [<c163a3b6>] ? apic_timer_interrupt+0x2a/0x30 [ 31.812741] [<c128f31e>] ? tty_ioctl+0x47e/0xa30 [ 31.812741] [<c11e0d66>] ? inode_has_perm+0x36/0x50 [ 31.812741] [<c11e13e8>] ? file_has_perm+0xa8/0xb0 [ 31.812741] [<c128eea0>] ? tty_check_change+0xe0/0xe0 [ 31.812741] [<c1106763>] ? do_vfs_ioctl+0x83/0x570 [ 31.812741] [<c11e4e46>] ? selinux_file_ioctl+0x56/0x110 [ 31.812741] [<c1108224>] sys_poll+0x54/0xb0 [ 31.812741] [<c1639b29>] syscall_call+0x7/0xb [ 31.812741] ---[ end trace 1d7d659b4aead681 ]--- With the two patches I'll attach to the next replies to this message, I've been able to get a task running on an isolated CPU with 0 timer interrupts. In my case, I also had to disable the clocksource watchdog, but only because TSC is not stable on my VM. This is really not a nohz/cpuset problem. There is one source of interference to cpu isolation this causes, which is the cputime flush IPI. Every time you run a command in the shell you get 3 - 4 IPIs sent to the nohz cpuset to flush the cputimes so that thread group times get computed correctly. That's not very nice :-) I've tried disabling the IPI send, just to see how it goes and as far as I've been able to tell you get bare metal like environment for a 100% cpu bound code with no interrupts. Of course. ps/top then show 0% cpu utilization for that task since without the IPI the times it spends on the CPU is not registered... that is a small price to pay in my eyes for bare metal performance on Linux, but what do I know? :-) Overall, way cool. Please keep it up ! GIlad -- Gilad Ben-Yossef Chief Coffee Drinker gilad@...yossef.com Israel Cell: +972-52-8260388 US Cell: +1-973-8260388 http://benyossef.com "If you take a class in large-scale robotics, can you end up in a situation where the homework eats your dog?" -- Jean-Baptiste Queru -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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