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From: Greg KH <gregkh@linuxfoundation.org>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: 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 11:27:54 +0200 [thread overview]
Message-ID: <20200925092754.GA2508526@kroah.com> (raw)
In-Reply-To: <87wo0j6nos.fsf@nanos.tec.linutronix.de>
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"
> >> + depends on HOTPLUG_CPU
> >> + def_bool n
> >
> > n is the default, no need to list it.
> >
> >> + help
> >> + In cpu hot plug path console lock acquire and release causes the
> >> + console to flush. If console lock is not free hot plug latency
> >> + increases. So make console flush configurable in hot plug path
> >> + and default disabled to help in cpu hot plug latencies.
> >
> > Why would you not want this option?
> >
> > Why isn't this just a bugfix?
>
> Because it's the normal behaviour of console lock and there are
> gazillion other ways to delay stuff in the hotplug 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 :(
> This #ifdef tinkering is just digusting especially as it just tackles an
> obvious way how to delay timer migration, but does not address the
> underlying root cause.
Agreed, thanks for putting it better than I did.
greg k-h
next prev parent reply other threads:[~2020-09-25 9:27 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 [this message]
2020-09-25 14:16 ` Adam Borowski
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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