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From: jim.cromie@gmail.com
To: "Ville Syrjälä" <ville.syrjala@linux.intel.com>
Cc: dri-devel@lists.freedesktop.org,
	LKML <linux-kernel@vger.kernel.org>,
	David Airlie <airlied@linux.ie>, Jason Baron <jbaron@akamai.com>,
	Thomas Zimmermann <tzimmermann@suse.de>
Subject: Re: [RFC PATCH 1/2] drm: RFC add choice to use dynamic debug in drm-debug
Date: Fri, 4 Dec 2020 12:20:21 -0700	[thread overview]
Message-ID: <CAJfuBxysOxnm846u71f0rQCH9NX-7AMe4brmiD0vqfGeQKuVOw@mail.gmail.com> (raw)
In-Reply-To: <X8pY/H512EMR3bUX@intel.com>

On Fri, Dec 4, 2020 at 8:42 AM Ville Syrjälä
<ville.syrjala@linux.intel.com> wrote:
>
> On Thu, Dec 03, 2020 at 08:53:17PM -0700, Jim Cromie wrote:
> > drm's debug system uses distinct categories of debug messages, mapped
> > to bits in drm.debug.  Currently, code does a lot of unlikely bit-mask
> > checks on drm.debug (in drm_debug_enabled), we can use dynamic debug
> > instead, and get all that jump_label goodness.
>
> whatis jump_label?

Sorry, I should have at least capitalized that, and spelled it differently

kernel/Makefile
118:obj-$(CONFIG_JUMP_LABEL) += jump_label.o

it is the hot-patching substrate underneath it all.
static-key, static-call, etc?
dynamic-debug uses static-key directly.



>
> One thing that bugs me about the current drm_dbg() stuff is that
> it's a function, and thus we pay the cost of setting up the
> arguments even when debugs are not enabled. I played around a bit
> with making it a macro again with the unlikely bit check moved
> into the macro. That did seem to make some of the asm a bit nicer
> where the debug stuff got shoved out the main codepath, but
> it did result in a slight net increase in code size. What I didn't
> have time to do is check if this has any measurable speed effect
> on eg. TEST_ONLY commits.
>
> And while doing that I started to ponder if we could use something
> like the alternate() instruction stuff to patch the code at runtime
> in order to turn all those debug checks into nops when debugging
> is not enabled. But I couldn't immediately find any generic
> infrastructure for it. So now I wonder if this jump_label is something
> like that?
>

this is the droid youre looking for ;-)

> >

> --
> Ville Syrjälä
> Intel

  reply	other threads:[~2020-12-04 19:21 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-12-04  3:53 [RFC PATCH 0/2] drm: use dynamic_debug Jim Cromie
2020-12-04  3:53 ` [RFC PATCH 1/2] drm: RFC add choice to use dynamic debug in drm-debug Jim Cromie
2020-12-04 15:42   ` Ville Syrjälä
2020-12-04 19:20     ` jim.cromie [this message]
2020-12-11 15:30   ` Ville Syrjälä
2020-12-17 21:31     ` jim.cromie
2020-12-04  3:53 ` [RFC PATCH 2/2] i915: POC use dynamic_debug_exec_queries to control pr_debugs in gvt Jim Cromie

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