linux-kernel - Re: [PATCH] ftrace: Allow configuring global trace buffer size (for dump-on-oops)

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Date:   Tue, 14 Nov 2017 11:28:52 +0000
From:   Chris Wilson <chris@...is-wilson.co.uk>
To:     linux-kernel@...r.kernel.org
Cc:     intel-gfx@...ts.freedesktop.org,
        "Steven Rostedt" <srostedt@...hat.com>,
        "Peter Zijlstra" <peterz@...radead.org>,
        "Ingo Molnar" <mingo@...e.hu>,
        "Tomi Sarvela" <tomi.p.sarvela@...el.com>,
        "Joonas Lahtinen" <joonas.lahtinen@...ux.intel.com>,
        "Daniel Vetter" <daniel.vetter@...ll.ch>
Subject: Re: [PATCH] ftrace: Allow configuring global trace buffer size (for
 dump-on-oops)

Quoting Chris Wilson (2017-11-13 13:07:08)
> We have recently turned on ftrace-dump-on-oops for i915's CI and an
> issue we have encountered is that the trace buffer size greatly exceeds
> the pstore capabilities; we get the tail of the oops but not the
> introduction.
> 
> Currently the global buffer size is controllable on the cmdline, but at
> the request of our CI sysadmin, we would like to add a control to the
> Kconfig as well. The rationale being the cmdline carries the temporary
> hacks that we want to eradicate, and we want to track the permanent
> configuration in .config.
> 
> I have kept the Kconfig option hidden from the user as the default
> should suffice for the majority of users; reserving the configuration
> for those that eschew the cmdline option.

Odd, by removing the prompt the default value will always override the
user value in .config.

I had to restore a 
	prompt "Global ftrace buffer size" if EXPERT
to keep it configurable.
-Chris