From: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
To: "Maciej W. Rozycki" <macro@orcam.me.uk>
Cc: Arnd Bergmann <arnd@arndb.de>,
Huacai Chen <chenhuacai@kernel.org>,
Huacai Chen <chenhuacai@loongson.cn>,
Jiaxun Yang <jiaxun.yang@flygoat.com>,
linux-arch@vger.kernel.org, linux-mips@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 0/4] Reinstate and improve MIPS `do_div' implementation
Date: Wed, 21 Apr 2021 14:01:48 +0200 [thread overview]
Message-ID: <20210421120148.GC8637@alpha.franken.de> (raw)
In-Reply-To: <alpine.DEB.2.21.2104200044060.44318@angie.orcam.me.uk>
On Tue, Apr 20, 2021 at 04:50:22AM +0200, Maciej W. Rozycki wrote:
> Hi,
>
> As Huacai has recently discovered the MIPS backend for `do_div' has been
> broken and inadvertently disabled with commit c21004cd5b4c ("MIPS: Rewrite
> <asm/div64.h> to work with gcc 4.4.0."). As it is code I have originally
> written myself and Huacai had issues bringing it back to life leading to a
> request to discard it even I have decided to step in.
>
> In the end I have fixed the code and measured its performance to be ~100%
> better on average than our generic code. I have decided it would be worth
> having the test module I have prepared for correctness evaluation as well
> as benchmarking, so I have included it with the series, also so that I can
> refer to the results easily.
>
> In the end I have included four patches on this occasion: 1/4 is the test
> module, 2/4 is an inline documentation fix/clarification for the `do_div'
> wrapper, 3/4 enables the MIPS `__div64_32' backend and 4/4 adds a small
> performance improvement to it.
>
> I have investigated a fifth change as a potential improvement where I
> replaced the call to `do_div64_32' with a DIVU instruction for cases where
> the high part of the intermediate divident is zero, but it has turned out
> to regress performance a little, so I have discarded it.
>
> Also a follow-up change might be worth having to reduce the code size and
> place `__div64_32' out of line for CC_OPTIMIZE_FOR_SIZE configurations,
> but I have not fully prepared such a change at this time. I did use the
> WIP form I have for performance evaluation however; see the figures quoted
> with 4/4.
>
> These changes have been verified with a DECstation system with an R3400
> MIPS I processor @40MHz and a MTI Malta system with a 5Kc MIPS64 processor
> @160MHz.
>
> See individual change descriptions and any additional discussions for
> further details.
>
> Questions, comments or concerns? Otherwise please apply.
series applied to mips-next.
Thomas.
--
Crap can work. Given enough thrust pigs will fly, but it's not necessarily a
good idea. [ RFC1925, 2.3 ]
next prev parent reply other threads:[~2021-04-21 12:52 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-20 2:50 [PATCH 0/4] Reinstate and improve MIPS `do_div' implementation Maciej W. Rozycki
2021-04-20 2:50 ` [PATCH 1/4] lib/math: Add a `do_div' test module Maciej W. Rozycki
2021-04-20 2:50 ` [PATCH 2/4] div64: Correct inline documentation for `do_div' Maciej W. Rozycki
2021-04-20 2:50 ` [PATCH 3/4] MIPS: Reinstate platform `__div64_32' handler Maciej W. Rozycki
2021-04-22 18:36 ` Guenter Roeck
2021-04-22 20:43 ` Maciej W. Rozycki
2021-04-20 2:50 ` [PATCH 4/4] MIPS: Avoid DIVU in `__div64_32' is result would be zero Maciej W. Rozycki
2021-04-21 16:05 ` H. Nikolaus Schaller
2021-04-21 16:16 ` Maciej W. Rozycki
2021-04-22 7:56 ` Thomas Bogendoerfer
2021-04-22 9:12 ` Maciej W. Rozycki
2021-04-22 11:08 ` Thomas Bogendoerfer
2021-04-22 20:47 ` Maciej W. Rozycki
2021-04-27 12:16 ` Maciej W. Rozycki
2021-04-22 11:17 ` Andreas Schwab
2021-04-21 12:01 ` Thomas Bogendoerfer [this message]
2021-04-21 13:12 ` [PATCH 0/4] Reinstate and improve MIPS `do_div' implementation Maciej W. Rozycki
2021-04-21 16:00 ` H. Nikolaus Schaller
2021-04-21 19:04 ` Maciej W. Rozycki
2021-04-22 5:53 ` H. Nikolaus Schaller
2021-04-22 13:39 ` Jiaxun Yang
2021-04-22 15:58 ` Maciej W. Rozycki
2021-04-22 16:00 ` H. Nikolaus Schaller
2021-04-22 16:55 ` Maciej W. Rozycki
2021-04-22 17:06 ` H. Nikolaus Schaller
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