linux-kernel - Re: TREE_SRCU slows hotplug by factor ~16

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Message-ID: <1493023382.6266.9.camel@gmx.de>
Date:   Mon, 24 Apr 2017 10:43:02 +0200
From:   Mike Galbraith <efault@....de>
To:     paulmck@...ux.vnet.ibm.com
Cc:     LKML <linux-kernel@...r.kernel.org>
Subject: Re: TREE_SRCU slows hotplug by factor ~16

On Mon, 2017-04-24 at 09:35 +0200, Mike Galbraith wrote:

> # tracer: nop
> #
> # entries-in-buffer/entries-written: 229332/229332   #P:8
> #
> #                              _-----=> irqs-off
> #                             / _----=> need-resched
> #                            | / _---=> hardirq/softirq
> #                            || / _--=> preempt-depth
> #                            ||| /     delay
> #           TASK-PID   CPU#  ||||    TIMESTAMP  FUNCTION
> #              | |       |   ||||       |         |
>  stress-cpu-hotp-2443  [004] ....   144.123608: synchronize_srcu: enter
>  stress-cpu-hotp-2443  [004] ....   144.123610: call_srcu: enter
>  stress-cpu-hotp-2443  [004] ....   144.123612: call_srcu: exit
>  stress-cpu-hotp-2443  [005] ....   144.139528: synchronize_srcu: exit

I probably could have sent a LOT less trace.

classic:

# tracer: nop
#
# entries-in-buffer/entries-written: 114688/114688   #P:8
#
#                              _-----=> irqs-off
#                             / _----=> need-resched
#                            | / _---=> hardirq/softirq
#                            || / _--=> preempt-depth
#                            ||| /     delay
#           TASK-PID   CPU#  ||||    TIMESTAMP  FUNCTION
#              | |       |   ||||       |         |
 stress-cpu-hotp-4337  [007] ....   174.082801: synchronize_srcu: enter
 stress-cpu-hotp-4337  [007] ....   174.082802: synchronize_srcu: exit
 stress-cpu-hotp-4337  [007] ....   174.082896: synchronize_srcu: enter
 stress-cpu-hotp-4337  [007] ....   174.082896: synchronize_srcu: exit
 stress-cpu-hotp-4337  [007] ....   174.082975: synchronize_srcu: enter
 stress-cpu-hotp-4337  [007] ....   174.082975: synchronize_srcu: exit
 stress-cpu-hotp-4337  [007] ....   174.083051: synchronize_srcu: enter
 stress-cpu-hotp-4337  [007] ....   174.083051: synchronize_srcu: exit
....