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Subject[RFC PATCH] kick ksoftirqd more often to please soft lockup detector
An experimental hack to tease out whether we are continuing to
run the softirq handler past the point of needing scheduling.

It allows only one trip through __do_softirq() as long as need_resched()
is set which hopefully creates the back pressure needed to get ksoftirqd

Targeted to address reports like the following that are produced
with i/o tests to a sas domain with a large number of disks (48+), and
lots of debugging enabled (slub_deubg, lockdep) that makes the
block+scsi softirq path more cpu-expensive than normal.

With this patch applied the softlockup detector seems appeased, but it
seems odd to need changes to kernel/softirq.c so maybe I have overlooked
something that needs changing at the block/scsi level?

BUG: soft lockup - CPU#3 stuck for 22s! [kworker/3:1:78]
Modules linked in: nls_utf8 ipv6 uinput sg iTCO_wdt iTCO_vendor_support ioatdma dca i2c_i801 i2c_core wmi sd_mod ahci libahci isci libsas libata scsi_transport_sas [last unloaded: scsi_wait_scan]
irq event stamp: 26260303
hardirqs last enabled at (26260302): [<ffffffff814becf4>] restore_args+0x0/0x30
hardirqs last disabled at (26260303): [<ffffffff814c60ee>] apic_timer_interrupt+0x6e/0x80
softirqs last enabled at (26220386): [<ffffffff81033edd>] __do_softirq+0x1ae/0x1bd
softirqs last disabled at (26220665): [<ffffffff814c696c>] call_softirq+0x1c/0x26
Modules linked in: nls_utf8 ipv6 uinput sg iTCO_wdt iTCO_vendor_support ioatdma dca i2c_i801 i2c_core wmi sd_mod ahci libahci isci libsas libata scsi_transport_sas [last unloaded: scsi_wait_scan]

Pid: 78, comm: kworker/3:1 Not tainted 3.3.0-rc3-7ada1dd-isci-3.0.183+ #1 Intel Corporation ROSECITY/ROSECITY
RIP: 0010:[<ffffffff814be8b6>] [<ffffffff814be8b6>] _raw_spin_unlock_irq+0x34/0x4b
RSP: 0000:ffff8800bb8c3c50 EFLAGS: 00000202
RAX: ffff8800375f3ec0 RBX: ffffffff814becf4 RCX: ffff8800bb8c3c00
RDX: 0000000000000001 RSI: ffff880035bbc348 RDI: ffff8800375f4588
RBP: ffff8800bb8c3c60 R08: 0000000000000000 R09: ffff880035aed150
R10: 0000000000018f3b R11: ffff8800bb8c39e0 R12: ffff8800bb8c3bc8
R13: ffffffff814c60f3 R14: ffff8800bb8c3c60 R15: 0000000000000000
FS: 0000000000000000(0000) GS:ffff8800bb8c0000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b
CR2: 0000000000f2e028 CR3: 00000000b11b3000 CR4: 00000000000406e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
Process kworker/3:1 (pid: 78, threadinfo ffff8800377d2000, task ffff8800375f3ec0)
ffff88003555f800 ffff88003555f800 ffff8800bb8c3cc0 ffffffffa00512c4
ffffffff814be8b2 ffff880035dfc000 ffff880035dfe000 000000000553a265
ffff8800bb8c3cb0 ffff88003555f800 ffff8800b20af200 ffff880035dfe000
Call Trace:
[<ffffffffa00512c4>] sas_queuecommand+0xa7/0x204 [libsas]
[<ffffffff814be8b2>] ? _raw_spin_unlock_irq+0x30/0x4b
[<ffffffff8132b6a9>] scsi_dispatch_cmd+0x1a2/0x24c
[<ffffffff813317a8>] ? spin_lock+0x9/0xb
[<ffffffff813333b0>] scsi_request_fn+0x3b1/0x3d9
[<ffffffff8124a19f>] __blk_run_queue+0x1d/0x1f
[<ffffffff8124b869>] blk_run_queue+0x26/0x3a
[<ffffffff813319a5>] scsi_run_queue+0x1fb/0x20a
[<ffffffff81332136>] scsi_next_command+0x3b/0x4c
[<ffffffff81332b66>] scsi_io_completion+0x205/0x44f
[<ffffffff813316b8>] ? spin_unlock_irqrestore+0x9/0xb
[<ffffffff8132b3ab>] scsi_finish_command+0xeb/0xf4
[<ffffffff81333a04>] scsi_softirq_done+0x112/0x11b
[<ffffffff812540ac>] blk_done_softirq+0x7e/0x96
[<ffffffff81033e0c>] __do_softirq+0xdd/0x1bd
[<ffffffff814c696c>] call_softirq+0x1c/0x26
[<ffffffff81003ce6>] do_softirq+0x4b/0xa5
[<ffffffff81034916>] irq_exit+0x55/0xc2
[<ffffffff814c6a9c>] smp_apic_timer_interrupt+0x7c/0x8a
[<ffffffff814c60f3>] apic_timer_interrupt+0x73/0x80
[<ffffffff814be8b6>] ? _raw_spin_unlock_irq+0x34/0x4b
[<ffffffffa00512c4>] sas_queuecommand+0xa7/0x204 [libsas]
[<ffffffff814be8b2>] ? _raw_spin_unlock_irq+0x30/0x4b
[<ffffffff8132b6a9>] scsi_dispatch_cmd+0x1a2/0x24c
[<ffffffff813317a8>] ? spin_lock+0x9/0xb
[<ffffffff813333b0>] scsi_request_fn+0x3b1/0x3d9
[<ffffffff8124a19f>] __blk_run_queue+0x1d/0x1f
[<ffffffff8125f3bb>] cfq_kick_queue+0x2f/0x41
[<ffffffff8104462e>] process_one_work+0x1c8/0x336
[<ffffffff81044599>] ? process_one_work+0x133/0x336
[<ffffffff81044306>] ? spin_lock_irq+0x9/0xb
[<ffffffff8125f38c>] ? cfq_init_queue+0x2a3/0x2a3
[<ffffffff81045fd9>] ? workqueue_congested+0x1e/0x1e
[<ffffffff81046085>] worker_thread+0xac/0x151
[<ffffffff81045fd9>] ? workqueue_congested+0x1e/0x1e
[<ffffffff8104a618>] kthread+0x8a/0x92
[<ffffffff8107654e>] ? trace_hardirqs_on_caller+0x16/0x16d
[<ffffffff814c6874>] kernel_thread_helper+0x4/0x10
[<ffffffff814becf4>] ? retint_restore_args+0x13/0x13
[<ffffffff8104a58e>] ? kthread_create_on_node+0x14d/0x14d
[<ffffffff814c6870>] ? gs_change+0x13/0x13

Cc: Peter Zijlstra <>
Cc: Jens Axboe <>
Cc: James Bottomley <>
Reported-by: Lukasz Dorau <>
Reported-by: Andrzej Jakowski <>
Not-yet-signed-off-by: Dan Williams <>
kernel/softirq.c | 2 +-
1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/kernel/softirq.c b/kernel/softirq.c
index 4eb3a0f..82a3f43 100644
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -255,7 +255,7 @@ restart:

pending = local_softirq_pending();
- if (pending && --max_restart)
+ if (pending && --max_restart && !need_resched())
goto restart;

if (pending)

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  Last update: 2012-02-27 21:25    [W:0.067 / U:6.636 seconds]
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