From: Itai Handler <itai.handler@gmail.com>
To: linux-rt-users@vger.kernel.org
Cc: Steven Rostedt <rostedt@goodmis.org>
Subject: aarch64 boot time increases with rt
Date: Mon, 13 Jul 2020 17:56:05 +0300 [thread overview]
Message-ID: <CAFpOueS0rvys4Q81D3HEYX2U1vM808qQ4w+z6QxCWi1KJBGXXQ@mail.gmail.com> (raw)
Hi,
I observed that aarch64 boot time increases considerably with rt
(PREEMPT_RT_FULL=y).
This is observable also in latest 4.19 rt (4.19.127-rt55).
Following is a fragment from kernel log (with rt) which shows that
bringing up 4 CPUs takes about 210 ms:
[ 0.120951] smp: Bringing up secondary CPUs ...
[ 0.184860] Detected VIPT I-cache on CPU1
[ 0.187344] CPU1: Booted secondary processor 0x0000000001 [0x410fd034]
[ 0.262931] Detected VIPT I-cache on CPU2
[ 0.263390] CPU2: Booted secondary processor 0x0000000002 [0x410fd034]
[ 0.329296] Detected VIPT I-cache on CPU3
[ 0.329872] CPU3: Booted secondary processor 0x0000000003 [0x410fd034]
[ 0.331557] smp: Brought up 1 node, 4 CPUs
Note that these times are from qemu, however the problem is also
noticeable on real hardware.
I traced the code and found that the slow down is caused in
workqueue_prepare_cpu().
This function creates the worker threads.
On real hardware, it takes about 8 ms to create each worker thread.
Before digging into it in more detail, I would like to hear your opinion.
Steven, what ftrace command line parameters do you recommend to use in
this case?
Thank you,
Itai Handler
next reply other threads:[~2020-07-13 14:56 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-13 14:56 Itai Handler [this message]
2020-07-14 1:20 ` aarch64 boot time increases with rt Steven Rostedt
2020-07-14 12:18 ` Itai Handler
2020-07-14 14:34 ` Steven Rostedt
2020-07-15 19:36 ` Steven Rostedt
2020-07-16 13:04 ` Itai Handler
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