All of lore.kernel.org
 help / color / mirror / Atom feed
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

             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

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=CAFpOueS0rvys4Q81D3HEYX2U1vM808qQ4w+z6QxCWi1KJBGXXQ@mail.gmail.com \
    --to=itai.handler@gmail.com \
    --cc=linux-rt-users@vger.kernel.org \
    --cc=rostedt@goodmis.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body. 
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.