On Fri, Jul 25, 2014 at 1:06 AM, Pranith Kumar <bobby.pr...@gmail.com> wrote:
>
> In rcu_report_qs_rsp(), I added a pr_info() call testing if any of the above
> conditions is true, in which case we can avoid calling wake_up(). It turns out
> that quite a few actually are. Most of the cases where we can avoid is
> condition 2
> above and condition 1 also occurs quite often. Condition 3 never happens.
>
A little more data. On an idle system there are about 2000 unnecessary
wake_up() calls every 5 minutes with the most common trace being the
follows:
[Fri Jul 25 02:05:49 2014] [<ffffffff8109f7c5>] rcu_report_qs_rnp+0x285/0x2c0
[Fri Jul 25 02:05:49 2014] [<ffffffff81838c09>] ? schedule_timeout+0x159/0x270
[Fri Jul 25 02:05:49 2014] [<ffffffff8109fa21>] force_qs_rnp+0x111/0x190
[Fri Jul 25 02:05:49 2014] [<ffffffff810a02c0>] ? synchronize_rcu_bh+0x50/0x50
[Fri Jul 25 02:05:49 2014] [<ffffffff810a2e5f>] rcu_gp_kthread+0x85f/0xa70
[Fri Jul 25 02:05:49 2014] [<ffffffff81086060>] ? __wake_up_sync+0x20/0x20
[Fri Jul 25 02:05:49 2014] [<ffffffff810a2600>] ? rcu_barrier+0x20/0x20
[Fri Jul 25 02:05:49 2014] [<ffffffff8106b4fb>] kthread+0xdb/0x100
[<ffffffff8106b420>]?kthread_create_on_node+0x180/0x180
[Fri Jul 25 02:05:49 2014] [<ffffffff81839dac>] ret_from_fork+0x7c/0xb0
[<ffffffff8106b420>] ?kthread_create_on_node+0x180/0x180
With rcutorture, there are about 2000 unnecessary wake_ups() every 3
minutes with the most common trace being:
[Fri Jul 25 02:18:30 2014] [<ffffffff8109f7c5>] rcu_report_qs_rnp+0x285/0x2c0
[Fri Jul 25 02:18:30 2014] [<ffffffff81078b15>] ? __update_cpu_load+0xe5/0x140
[<ffffffffa09dc230>] ?rcu_read_delay+0x50/0x80 [rcutorture]
[<ffffffff810a3728>]rcu_process_callbacks+0x6b8/0x7e0
--
Pranith
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