linux-kernel - Re: [PATCH v7 4/8] sched: nominate preferred wakeup cpu

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Message-ID: <20081219222709.GN2351@elte.hu>
Date:	Fri, 19 Dec 2008 23:27:09 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Andrew Morton <akpm@...ux-foundation.org>,
	Yinghai Lu <yinghai@...nel.org>
Cc:	svaidy@...ux.vnet.ibm.com, linux-kernel@...r.kernel.org,
	suresh.b.siddha@...el.com, venkatesh.pallipadi@...el.com,
	a.p.zijlstra@...llo.nl, dipankar@...ibm.com,
	balbir@...ux.vnet.ibm.com, vatsa@...ux.vnet.ibm.com,
	ego@...ibm.com, andi@...stfloor.org, davecb@....com,
	tconnors@...ro.swin.edu.au, maxk@...lcomm.com,
	gregory.haskins@...il.com, pavel@...e.cz, rusty@...tcorp.com.au
Subject: Re: [PATCH v7 4/8] sched: nominate preferred wakeup cpu


* Andrew Morton <akpm@...ux-foundation.org> wrote:

> On Fri, 19 Dec 2008 13:55:08 -0800
> Andrew Morton <akpm@...ux-foundation.org> wrote:
> 
> > On Thu, 18 Dec 2008 23:26:22 +0530
> > Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com> wrote:
> > 
> > > When the system utilisation is low and more cpus are idle,
> > > then the process waking up from sleep should prefer to
> > > wakeup an idle cpu from semi-idle cpu package (multi core
> > > package) rather than a completely idle cpu package which
> > > would waste power.
> > > 
> > > Use the sched_mc balance logic in find_busiest_group() to
> > > nominate a preferred wakeup cpu.
> > > 
> > > This info can be sored in appropriate sched_domain, but
> > > updating this info in all copies of sched_domain is not
> > > practical.  Hence this information is stored in root_domain
> > > struct which is one copy per partitioned sched domain.
> > > The root_domain can be accessed from each cpu's runqueue
> > > and there is one copy per partitioned sched domain.
> > > 
> > 
> > kernel/sched.c: In function 'find_busiest_group':
> > kernel/sched.c:3403: warning: passing argument 1 of '__first_cpu' from incompatible pointer type
> > 
> > 
> > kernel/sched.c: In function 'schedule':
> > kernel/sched.c:3679: warning: 'active_balance' may be used uninitialized in this function
> > 
> 
> I left those unfixed and...
> 
> [   62.307607] initcall init_nfsd+0x0/0xe2 [nfsd] returned 0 after 251 usecs
> [   62.399426] NFSD: Using /var/lib/nfs/v4recovery as the NFSv4 state recovery directory
> [   74.009934] divide error: 0000 [#1] SMP 
> [   74.010085] last sysfs file: /sys/devices/pci0000:00/0000:00:02.0/0000:01:00.0/0000:02:02.0/0000:05:00.1/irq
> [   74.010147] CPU 1 
> [   74.010241] Modules linked in: nfsd auth_rpcgss exportfs lockd nfs_acl autofs4 hidp rfcomm l2cap bluetooth sunrpc ipv6 dm_mirror dm_region_hash dm_log dm_multipath dm_mod rfkill input_polldev sbs sbshc battery ac parport_pc lp parport snd_hda_codec_realtek sg snd_hda_intel floppy snd_hda_codec snd_seq_dummy snd_seq_oss snd_seq_midi_event snd_seq snd_seq_device ide_cd_mod cdrom snd_pcm_oss snd_mixer_oss serio_raw snd_pcm button shpchp snd_timer i2c_i801 i2c_core snd soundcore snd_page_alloc pcspkr ehci_hcd ohci_hcd uhci_hcd
> [   74.012821] Pid: 0, comm: swapper Not tainted 2.6.28-rc9-mm1 #1
> [   74.012875] RIP: 0010:[<ffffffff802375d8>]  [<ffffffff802375d8>] tg_shares_up+0x113/0x1f1
> [   74.012982] RSP: 0018:ffff88025e057d88  EFLAGS: 00010246
> [   74.013038] RAX: 0000000000000000 RBX: ffff880028063900 RCX: ffff880028058dc0
> [   74.013095] RDX: 0000000000000000 RSI: 0000000000000000 RDI: 00000000000000ff
> [   74.013152] RBP: ffff88025e057dd8 R08: 0000000000000000 R09: 0000000000000000
> [   74.013209] R10: ffff880028067640 R11: 0000000000000022 R12: ffff880028063900
> [   74.013264] R13: ffffffff802374c5 R14: ffffffff8022c546 R15: ffffffff8079b4a0
> [   74.013321] FS:  0000000000000000(0000) GS:ffff88025e0385c0(0000) knlGS:0000000000000000
> [   74.013381] CS:  0010 DS: 0018 ES: 0018 CR0: 000000008005003b
> [   74.013435] CR2: 00007fdb795af8f0 CR3: 0000000000201000 CR4: 00000000000006e0
> [   74.013489] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> [   74.013545] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
> [   74.013602] Process swapper (pid: 0, threadinfo ffff88025e050000, task ffff88025e03f870)
> [   74.013661] Stack:
> [   74.013708]  0000000000000000 ffff880028063a00 0000000000000000 0000000000000000
> [   74.013893]  0000000000000008 ffffffff8079b4a0 ffff880028063900 ffffffff802374c5
> [   74.013893]  ffffffff8022c546 0000000000000030 ffff88025e057e08 ffffffff8022c530
> [   74.013893] Call Trace:
> [   74.013893]  <IRQ> <0> [<ffffffff802374c5>] ? tg_shares_up+0x0/0x1f1
> [   74.013893]  [<ffffffff8022c546>] ? tg_nop+0x0/0x8
> [   74.013893]  [<ffffffff8022c530>] walk_tg_tree+0x5f/0x75
> [   74.013893]  [<ffffffff8022c65c>] update_shares+0x46/0x4a
> [   74.013893]  [<ffffffff80235fe4>] run_rebalance_domains+0x192/0x522
> [   74.013893]  [<ffffffff802543eb>] ? getnstimeofday+0x3d/0x9e
> [   74.013893]  [<ffffffff8052bd73>] ? _spin_unlock_irq+0x9/0xc
> [   74.013893]  [<ffffffff8024057f>] __do_softirq+0xa3/0x164
> [   74.013893]  [<ffffffff8020d0bc>] call_softirq+0x1c/0x28
> [   74.013893]  [<ffffffff8020e19d>] do_softirq+0x31/0x73
> [   74.013893]  [<ffffffff802402ca>] irq_exit+0x3f/0x41
> [   74.013893]  [<ffffffff8021e71d>] smp_apic_timer_interrupt+0x94/0xad
> [   74.013893]  [<ffffffff8020caf3>] apic_timer_interrupt+0x13/0x20
> [   74.013893]  <EOI> <0>Code: 8b 47 08 4a 8b 0c 00 48 85 c9 0f 84 c3 00 00 00 49 8b 47 10 4a 8b 04 00 48 8b 80 a8 00 00 00 48 85 c0 74 13 48 0f af 45 c8 31 d2 <48> f7 75 c0 49 89 c6 48 89 c6 eb 16 48 63 55 d0 48 8b 45 c8 45 
> [   74.013893] RIP  [<ffffffff802375d8>] tg_shares_up+0x113/0x1f1
> [   74.013893]  RSP <ffff88025e057d88>
> [   74.020022] ---[ end trace 2fc4046e394f2312 ]---
> [   74.020188] Kernel panic - not syncing: Fatal exception in interrupt
> 
> config: http://userweb.kernel.org/~akpm/config-akpm2.txt
> 
> I'll try hacking some div-by-zero avoidance into update_group_shares_cpu().

hm, weird - Yinghai noticed this crash in -tip and we have that patch 
zapped from all -*-next branches already.

	Ingo
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