Messages in this thread Patch in this message | | | Date | Sat, 17 Nov 2012 14:01:29 +0100 | From | Zlatko Calusic <> | Subject | High context switch rate, ksoftirqd's chewing cpu |
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Hello Tejun et al.
This week I spent some hours tracking a regression in 3.7 kernel that was producing high context switch rate on one of my machines. I carefully bisected between 3.6 and 3.7-rc1 and eventually found this commit a culprit:
commit e7c2f967445dd2041f0f8e3179cca22bb8bb7f79 Author: Tejun Heo <tj@kernel.org> Date: Tue Aug 21 13:18:24 2012 -0700
workqueue: use mod_delayed_work() instead of __cancel + queue
Now that mod_delayed_work() is safe to call from IRQ handlers, __cancel_delayed_work() followed by queue_delayed_work() can be replaced with mod_delayed_work().
Most conversions are straight-forward except for the following.
* net/core/link_watch.c: linkwatch_schedule_work() was doing a quite elaborate dancing around its delayed_work. Collapse it such that linkwatch_work is queued for immediate execution if LW_URGENT and existing timer is kept otherwise.
Signed-off-by: Tejun Heo <tj@kernel.org> Cc: "David S. Miller" <davem@davemloft.net> Cc: Tomi Valkeinen <tomi.valkeinen@ti.com>
Then I carefully reverted chunk by chunk to find out what exact change is responsible for the regression. You can find it attached as wq.patch (to preserve whitespace). Very simple modification with wildly different behavior on only one of my machines, weird. I'm also attaching ctxt/s graph that shows the impact nicely. I'll gladly provide any additional info that could help you resolve this.
Please Cc: on reply (not subscribed to lkml).
Regards, -- Zlatko diff --git a/block/blk-core.c b/block/blk-core.c index 4b4dbdf..4b8b606 100644 --- a/block/blk-core.c +++ b/block/blk-core.c @@ -319,10 +319,8 @@ EXPORT_SYMBOL(__blk_run_queue); */ void blk_run_queue_async(struct request_queue *q) { - if (likely(!blk_queue_stopped(q))) { - __cancel_delayed_work(&q->delay_work); - queue_delayed_work(kblockd_workqueue, &q->delay_work, 0); - } + if (likely(!blk_queue_stopped(q))) + mod_delayed_work(kblockd_workqueue, &q->delay_work, 0); } EXPORT_SYMBOL(blk_run_queue_async); [unhandled content-type:image/png] | |