From: Brad Boyer <flar@allandria.com>
To: Michael Schmitz <schmitzmic@gmail.com>
Cc: Finn Thain <fthain@linux-m68k.org>,
linux-m68k@vger.kernel.org, geert@linux-m68k.org,
linux-ide@vger.kernel.org, ALeX Kazik <alex@kazik.de>
Subject: Re: [PATCH RFC 1/2] m68k: io_mm.h: conditionalize ISA address translation on Atari
Date: Sun, 6 Jun 2021 16:51:06 -0700 [thread overview]
Message-ID: <20210606235106.GA10846@allandria.com> (raw)
In-Reply-To: <460124e6-6ac3-4b94-43de-ebff5cb50cf8@gmail.com>
On Sun, Jun 06, 2021 at 05:42:30PM +1200, Michael Schmitz wrote:
> >Would (port & ~1) be faster than (port - 1) here?
>
> Perhaps it would - I'd hope the compiler will pick the most efficient
> solution here.
I'm pretty sure the compiler couldn't do that optimization. Without
more context, those two statements are not equivalent. I don't see
how the compiler could know that.
Looking at the 68040 manual, the instruction timing of ANDI and SUBQ
is mostly the same (except for immediate addressing, where ANDI is
slower). The ANDI is also going to take up extra bytes in the code
to put the bitmask in an extension word. BCLR can be faster than
ANDI or SUBQ in some cases, but it's slower in others. It also needs
an extension word when using an immediate value for the bit number.
If you presume port is in a data register, then ANDI and SUBQ have
the same timing and BCLR is slower. At that point, the difference
between ANDI and SUBQ is the size of the instruction which would
favor using SUBQ. I haven't checked if other m68k chips have similar
timings.
Unless I missed something, I don't see a better way to do the
equivalent of the and with a constant bitmask.
Brad Boyer
flar@allandria.com
next prev parent reply other threads:[~2021-06-06 23:51 UTC|newest]
Thread overview: 86+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-25 9:06 [PATCH] m68k/mac: Replace macide driver with generic platform driver Finn Thain
2021-04-25 10:25 ` John Paul Adrian Glaubitz
2021-04-26 7:37 ` Finn Thain
2021-04-26 7:48 ` John Paul Adrian Glaubitz
2021-04-27 1:51 ` Michael Schmitz
2021-04-27 3:47 ` Finn Thain
2021-04-27 19:54 ` Michael Schmitz
2021-04-28 6:53 ` Geert Uytterhoeven
2021-06-01 3:32 ` Michael Schmitz
2021-06-01 7:55 ` Michael Schmitz
2021-06-01 8:43 ` Geert Uytterhoeven
2021-06-01 21:05 ` Michael Schmitz
2021-06-02 5:21 ` [PATCH RFC 0/2] Fix m68k multiplatform ISA support Michael Schmitz
2021-06-02 5:21 ` [PATCH RFC 1/2] m68k: io_mm.h: conditionalize ISA address translation on Atari Michael Schmitz
2021-06-03 8:23 ` Finn Thain
2021-06-04 0:19 ` Michael Schmitz
2021-06-04 5:55 ` Finn Thain
2021-06-04 7:30 ` Michael Schmitz
2021-06-04 22:49 ` Brad Boyer
2021-06-05 1:41 ` Michael Schmitz
2021-06-05 6:04 ` Brad Boyer
2021-06-05 22:05 ` Michael Schmitz
2021-06-06 2:18 ` Michael Schmitz
2021-06-06 4:53 ` Finn Thain
2021-06-06 5:42 ` Michael Schmitz
2021-06-06 23:51 ` Brad Boyer [this message]
2021-06-06 5:54 ` [PATCH RFC 0/2] Add APNE PCMCIA 100 Mbit support Michael Schmitz
2021-06-06 5:54 ` [PATCH RFC 1/2] m68k: io_mm.h - add APNE 100 MBit support Michael Schmitz
2021-06-07 8:01 ` Geert Uytterhoeven
2021-06-07 8:20 ` Michael Schmitz
2021-06-07 11:15 ` Geert Uytterhoeven
2021-06-07 19:57 ` Michael Schmitz
2021-06-08 6:42 ` Geert Uytterhoeven
2021-06-08 21:55 ` Michael Schmitz
2021-06-09 6:33 ` Geert Uytterhoeven
2021-06-08 21:56 ` Michael Schmitz
2021-06-06 5:54 ` [PATCH RFC 2/2] net/8390: apne.c - add 100 Mbit support to apne.c driver Michael Schmitz
2021-06-06 12:42 ` kernel test robot
2021-06-07 8:08 ` Geert Uytterhoeven
2021-06-07 8:40 ` Michael Schmitz
2021-06-07 8:46 ` ALeX Kazik
2021-06-08 3:10 ` Michael Schmitz
2021-06-07 8:37 ` Geert Uytterhoeven
2021-06-07 12:56 ` Geert Uytterhoeven
2021-06-13 21:53 ` Michael Schmitz
2021-06-09 7:36 ` [PATCH v1 0/2] Add APNE PCMCIA 100 Mbit support Michael Schmitz
2021-06-09 7:36 ` [PATCH v1 1/2] m68k: io_mm.h - add APNE 100 MBit support Michael Schmitz
2021-06-09 8:04 ` Andreas Schwab
2021-06-09 21:54 ` Michael Schmitz
2021-06-10 1:09 ` Finn Thain
2021-06-10 7:32 ` Geert Uytterhoeven
2021-06-11 2:15 ` Michael Schmitz
2021-06-10 8:53 ` Andreas Schwab
2021-06-09 7:36 ` [PATCH v1 2/2] net/8390: apne.c - add 100 Mbit support to apne.c driver Michael Schmitz
2021-06-10 2:09 ` [PATCH v2 0/2] Add APNE PCMCIA 100 Mbit support Michael Schmitz
2021-06-10 2:09 ` [PATCH v2 1/2] m68k: io_mm.h - add APNE 100 MBit support Michael Schmitz
2021-06-10 2:09 ` [PATCH v2 2/2] net/8390: apne.c - add 100 Mbit support to apne.c driver Michael Schmitz
2021-06-16 21:11 ` [PATCH v2 0/2] Add APNE PCMCIA 100 Mbit support ALeX Kazik
2021-06-17 1:10 ` Michael Schmitz
2021-06-04 7:54 ` [PATCH RFC 1/2] m68k: io_mm.h: conditionalize ISA address translation on Atari Geert Uytterhoeven
2021-06-04 21:36 ` Michael Schmitz
2021-06-04 23:31 ` Finn Thain
2021-06-05 0:24 ` Finn Thain
2021-06-05 3:48 ` Michael Schmitz
2021-06-09 6:35 ` Geert Uytterhoeven
2021-06-09 7:20 ` Michael Schmitz
2021-06-02 5:21 ` [PATCH RFC 2/2] m68k: setup_mm.c: set isa_sex for Atari if ATARI_ROM_ISA not used Michael Schmitz
2021-06-02 7:09 ` Geert Uytterhoeven
2021-06-02 8:21 ` Michael Schmitz
2021-06-03 8:29 ` Finn Thain
2021-06-04 3:02 ` Michael Schmitz
2021-06-03 3:43 ` [PATCH RFC 0/2] Fix m68k multiplatform ISA support Michael Schmitz
2021-06-03 7:09 ` Geert Uytterhoeven
2021-06-04 0:22 ` Michael Schmitz
2021-06-06 5:28 ` [PATCH] m68k: Fix " Michael Schmitz
2021-06-07 7:49 ` Geert Uytterhoeven
2021-06-07 8:17 ` Michael Schmitz
2021-06-09 7:22 ` [PATCH v2] m68k: io_mm.h: conditionalize ISA address translation on Atari Michael Schmitz
2021-06-09 7:57 ` Andreas Schwab
2021-06-09 21:43 ` Michael Schmitz
2021-06-10 2:04 ` [PATCH v3] " Michael Schmitz
2021-04-27 8:11 ` [PATCH] m68k/mac: Replace macide driver with generic platform driver Sergei Shtylyov
2021-04-27 8:36 ` John Paul Adrian Glaubitz
2021-04-27 19:29 ` Michael Schmitz
2021-04-25 22:24 ` Michael Schmitz
2021-04-26 7:35 ` Finn Thain
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