From: Adam Borowski <kilobyte@angband.pl>
To: Greg KH <gregkh@linuxfoundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>,
Prasad Sodagudi <psodagud@codeaurora.org>,
rostedt@goodmis.org, pmladek@suse.com,
sergey.senozhatsky@gmail.com, linux-kernel@vger.kernel.org,
tkjos@google.com, Mohammed Khajapasha <mkhaja@codeaurora.org>
Subject: Re: [PATCH 2/2] printk: Make the console flush configurable in hotplug path
Date: Fri, 25 Sep 2020 16:16:57 +0200 [thread overview]
Message-ID: <20200925141657.GA6325@angband.pl> (raw)
In-Reply-To: <20200925092754.GA2508526@kroah.com>
On Fri, Sep 25, 2020 at 11:27:54AM +0200, Greg KH wrote:
> On Thu, Sep 24, 2020 at 08:21:07PM +0200, Thomas Gleixner wrote:
> > On Thu, Sep 24 2020 at 08:33, Greg KH wrote:
> > > On Wed, Sep 23, 2020 at 05:08:32PM -0700, Prasad Sodagudi wrote:
> > >> +config CONSOLE_FLUSH_ON_HOTPLUG
> > >> + bool "Enable console flush configurable in hot plug code path"
> > CPU hotplug is not meant to be a high speed operation and if people
> > think they need it to be fast then its pretty much guaranteed that they
> > want it for the completely wrong reasons.
>
> Odds are, it's the big/little systems that are trying to use cpu hotplug
> for this type of thing :(
Just a bit of info:
My MT6797X (10 core: 4×A53 + 4×A53 + 2×A72), flickers its cores this way:
the right-hand piece is CPUs, one character per core: bars show utilization,
"o" stands for offline; every line is 0.1 second interval.
topline -i 0.1
mmcblk(⠀) (oooo▄▆oo▅o)
mmcblk(⠀) (oooo▅▄oooo)
mmcblk(⠀) (oooo▆▆oooo)
mmcblk(⠀) (oooo▅ooo▆o)
mmcblk(⠀) (oooo▆▆oo▄o)
mmcblk(⠀) (oooo▆▇oooo)
mmcblk(⠀) (oooo▇ooo▅o)
mmcblk(⠀) (oooo▆ooo█o)
mmcblk(⠀) (oooo▆ooo▄o)
mmcblk(⠀) (oooo▅ooo▆o)
mmcblk(⠀) (oooo▆ooo▅o)
mmcblk(⠀) (oooo▄ooo▇o)
mmcblk(⠀) (oooo▇▆oo▆o)
mmcblk(⠀) (oooo▆ooo▅o)
mmcblk(⠀) (oooo▅▆oooo)
mmcblk(⠀) (oooo▆█oooo)
mmcblk(⠀) (oooo▆▇oooo)
mmcblk(⠀) (oooo▆▆oooo)
mmcblk(⠀) (oooo▅▆oooo)
mmcblk(⠀) (oooo▆▅oooo)
mmcblk(⠀) (oooo▆ooo▆o)
mmcblk(⠀) (oooo▆ooo▇o)
mmcblk(⢀) (oooo▆▇oo▆o)
mmcblk(⠀) (oooo▄ooo▆o)
mmcblk(⠀) (oooo▆ooo█o)
mmcblk(⠀) (oooo▄ooo▇o)
mmcblk(⠀) (oooo▄▆oooo)
mmcblk(⠀) (oooo▆▆oooo)
So it's on the order of a few ons/offs per second.
The offline CPUs are "present" and "offline"; not sure if this means hotplug
or not (I'd expect dropping from "present" to "possible", but I don't know
these parts).
Meow!
--
⢀⣴⠾⠻⢶⣦⠀
⣾⠁⢠⠒⠀⣿⡁ in the beginning was the boot and root floppies and they were good.
⢿⡄⠘⠷⠚⠋⠀ -- <willmore> on #linux-sunxi
⠈⠳⣄⠀⠀⠀⠀
next prev parent reply other threads:[~2020-09-25 14:17 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-24 0:08 [PATCH 1/2] genirq/cpuhotplug: Reduce logging level for couple of prints Prasad Sodagudi
2020-09-24 0:08 ` [PATCH 2/2] printk: Make the console flush configurable in hotplug path Prasad Sodagudi
2020-09-24 6:33 ` Greg KH
2020-09-24 18:21 ` Thomas Gleixner
2020-09-25 9:27 ` Greg KH
2020-09-25 14:16 ` Adam Borowski [this message]
2020-09-25 22:55 ` Thomas Gleixner
2020-09-28 2:05 ` psodagud
2020-09-28 12:50 ` Greg KH
2020-09-30 14:36 ` Petr Mladek
2020-09-24 6:38 ` Sergey Senozhatsky
2020-09-30 13:57 ` Petr Mladek
2020-09-24 6:31 ` [PATCH 1/2] genirq/cpuhotplug: Reduce logging level for couple of prints Greg KH
2020-09-24 18:08 ` Thomas Gleixner
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