From: Geert Uytterhoeven <geert@linux-m68k.org>
To: Doug Anderson <dianders@chromium.org>
Cc: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>,
dri-devel <dri-devel@lists.freedesktop.org>,
Linux-Renesas <linux-renesas-soc@vger.kernel.org>,
Andrzej Hajda <a.hajda@samsung.com>,
Neil Armstrong <narmstrong@baylibre.com>,
Jonas Karlman <jonas@kwiboo.se>,
Jernej Skrabec <jernej.skrabec@siol.net>,
Stephen Boyd <swboyd@chromium.org>
Subject: Re: [RFC PATCH 04/11] drm/bridge: ti-sn65dsi86: Use bitmask to store valid rates
Date: Wed, 24 Mar 2021 09:47:05 +0100 [thread overview]
Message-ID: <CAMuHMdXarCH4rP56HA5hxZ5heyotMD+_KraHu5r35baOe=MHug@mail.gmail.com> (raw)
In-Reply-To: <CAD=FV=UDd9LC-sMEk0hn10roeM+Cz6VNekcZomkQXLhfw0-4wA@mail.gmail.com>
Hi Doug,
On Tue, Mar 23, 2021 at 10:10 PM Doug Anderson <dianders@chromium.org> wrote:
> On Sun, Mar 21, 2021 at 8:02 PM Laurent Pinchart
> <laurent.pinchart+renesas@ideasonboard.com> wrote:
> >
> > The valid rates are stored in an array of 8 booleans. Replace it with a
> > bitmask to save space.
>
> I'm curious: do you have evidence that this does anything useful? I
> guess you're expecting it to save .text space, right? Stack usage and
> execution time differences should be irrelevant--it's not in a
> critical section and the difference should be tiny anyway. As far as
> .text segment goes, it's not obvious to me that the compiler will use
> fewer instructions to manipulate bits compared to booleans.
>
> Doing a super simple "ls -ah" on vmlinux (unstripped):
>
> Before: 224820232 bytes
> After: 224820376 bytes
>
> ...so your change made it _bigger_. OK, so running "strip
> --strip-debug" on those:
>
> Before: 26599464 bytes
> After: 26599464 bytes
I've been surprised by the counter-intuitive impact of similar changes
before, too. The result may also differ a lot between arm32 or arm64.
> ...so exactly the same. I tried finding some evidence using "readelf -ah":
>
> Before:
> [ 2] .text PROGBITS ffffffc010010000 00020000
> 0000000000b03508 0000000000000000 WAX 0 0 65536
> [ 3] .rodata PROGBITS ffffffc010b20000 00b30000
> 00000000002e84b3 0000000000000000 WAMS 0 0 4096
>
> After:
> [ 2] .text PROGBITS ffffffc010010000 00020000
> 0000000000b03508 0000000000000000 WAX 0 0 65536
> [ 3] .rodata PROGBITS ffffffc010b20000 00b30000
> 00000000002e84b3 0000000000000000 WAMS 0 0 4096
>
> Maybe you have some evidence showing an improvement? Ah, OK. I
> disassembled ti_sn_bridge_enable() and your patch saves 12 bytes, but
> I guess maybe alignment washes it out in reality...
Yes, arm64 is bad w.r.t. this.
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
next prev parent reply other threads:[~2021-03-24 8:48 UTC|newest]
Thread overview: 56+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-22 3:01 [RFC PATCH 00/11] drm/bridge: ti-sn65dsi86: Support DisplayPort mode Laurent Pinchart
2021-03-22 3:01 ` [RFC PATCH 01/11] dt-bindings: drm/bridge: ti-sn65dsi8: Make enable GPIO optional Laurent Pinchart
2021-03-22 10:29 ` Jagan Teki
2021-03-23 7:10 ` Stephen Boyd
2021-03-23 21:08 ` Doug Anderson
2021-03-27 16:42 ` Rob Herring
2021-03-22 3:01 ` [RFC PATCH 02/11] drm/bridge: ti-sn65dsi86: " Laurent Pinchart
2021-03-22 10:29 ` Jagan Teki
2021-03-23 7:10 ` Stephen Boyd
2021-03-23 21:08 ` Doug Anderson
2021-03-22 3:01 ` [RFC PATCH 03/11] drm/bridge: ti-sn65dsi86: Unregister AUX adapter in remove() Laurent Pinchart
2021-03-23 7:10 ` Stephen Boyd
2021-03-23 21:08 ` Doug Anderson
2021-03-23 21:41 ` Laurent Pinchart
2021-03-23 22:55 ` Doug Anderson
2021-03-23 23:02 ` Laurent Pinchart
2021-03-26 0:43 ` Doug Anderson
2021-03-26 1:01 ` Laurent Pinchart
2021-03-22 3:01 ` [RFC PATCH 04/11] drm/bridge: ti-sn65dsi86: Use bitmask to store valid rates Laurent Pinchart
2021-03-23 7:11 ` Stephen Boyd
2021-03-23 21:08 ` Doug Anderson
2021-03-23 21:45 ` Laurent Pinchart
2021-03-23 22:45 ` Doug Anderson
2021-03-24 8:47 ` Geert Uytterhoeven [this message]
2021-03-22 3:01 ` [RFC PATCH 05/11] drm/bridge: ti-sn65dsi86: Wrap panel with panel-bridge Laurent Pinchart
2021-03-22 10:19 ` Jagan Teki
2021-03-23 7:14 ` Stephen Boyd
2021-03-23 21:50 ` Laurent Pinchart
2021-03-24 22:44 ` Doug Anderson
2021-03-26 1:06 ` Laurent Pinchart
2021-03-22 3:01 ` [RFC PATCH 06/11] drm/bridge: ti-sn65dsi86: Group code in sections Laurent Pinchart
2021-03-23 7:14 ` Stephen Boyd
2021-03-24 22:44 ` Doug Anderson
2021-03-22 3:01 ` [RFC PATCH 07/11] drm/bridge: ti-sn65dsi86: Split connector creation to a function Laurent Pinchart
2021-03-23 7:15 ` Stephen Boyd
2021-03-24 22:44 ` Doug Anderson
2021-03-22 3:01 ` [RFC PATCH 08/11] drm/bridge: ti-sn65dsi86: Implement bridge connector operations Laurent Pinchart
2021-03-23 7:15 ` Stephen Boyd
2021-03-24 22:46 ` Doug Anderson
2021-03-26 1:40 ` Laurent Pinchart
2021-03-22 3:01 ` [RFC PATCH 09/11] drm/bridge: ti-sn65dsi86: Make connector creation optional Laurent Pinchart
2021-03-22 3:01 ` [RFC PATCH 10/11] drm/bridge: ti-sn65dsi86: Support DisplayPort (non-eDP) mode Laurent Pinchart
2021-03-24 22:47 ` Doug Anderson
2021-06-23 13:59 ` Laurent Pinchart
2022-02-23 18:04 ` Kieran Bingham
2022-02-23 18:20 ` Doug Anderson
2022-03-04 15:49 ` Laurent Pinchart
2021-03-22 3:01 ` [RFC PATCH 11/11] drm/bridge: ti-sn65dsi86: Support hotplug detection Laurent Pinchart
2021-03-23 7:21 ` Stephen Boyd
2021-03-24 22:47 ` Doug Anderson
2021-06-23 23:25 ` Laurent Pinchart
2021-06-23 23:51 ` Doug Anderson
2022-02-23 17:43 ` Kieran Bingham
2022-02-23 18:25 ` Doug Anderson
2022-03-04 15:45 ` Kieran Bingham
2022-03-04 16:30 ` Doug Anderson
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