From: Jisheng Zhang <jszhang@kernel.org>
To: Paul Walmsley <paul.walmsley@sifive.com>,
Palmer Dabbelt <palmer@dabbelt.com>,
Albert Ou <aou@eecs.berkeley.edu>
Cc: linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org,
Eric Biggers <ebiggers@kernel.org>,
Conor Dooley <conor.dooley@microchip.com>,
Qingfang DENG <dqfext@gmail.com>
Subject: [PATCH v4 0/2] riscv: enable EFFICIENT_UNALIGNED_ACCESS and DCACHE_WORD_ACCESS
Date: Mon, 25 Dec 2023 12:42:05 +0800 [thread overview]
Message-ID: <20231225044207.3821-1-jszhang@kernel.org> (raw)
Some riscv implementations such as T-HEAD's C906, C908, C910 and C920
support efficient unaligned access, for performance reason we want
to enable HAVE_EFFICIENT_UNALIGNED_ACCESS on these platforms. To
avoid performance regressions on non efficient unaligned access
platforms, HAVE_EFFICIENT_UNALIGNED_ACCESS can't be globally selected.
To solve this problem, runtime code patching based on the detected
speed is a good solution. But that's not easy, it involves lots of
work to modify vairous subsystems such as net, mm, lib and so on.
This can be done step by step.
So let's take an easier solution: add support to efficient unaligned
access and hide the support under NONPORTABLE.
patch1 introduces RISCV_EFFICIENT_UNALIGNED_ACCESS which depends on
NONPORTABLE, if users know during config time that the kernel will be
only run on those efficient unaligned access hw platforms, they can
enable it. Obviously, generic unified kernel Image shouldn't enable it.
patch2 adds support DCACHE_WORD_ACCESS when MMU and
RISCV_EFFICIENT_UNALIGNED_ACCESS.
Below test program and step shows how much performance can be improved:
$ cat tt.c
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
#define ITERATIONS 1000000
#define PATH "123456781234567812345678123456781"
int main(void)
{
unsigned long i;
struct stat buf;
for (i = 0; i < ITERATIONS; i++)
stat(PATH, &buf);
return 0;
}
$ gcc -O2 tt.c
$ touch 123456781234567812345678123456781
$ time ./a.out
Per my test on T-HEAD C910 platforms, the above test performance is
improved by about 7.5%.
Since v3:
- adopt Eric's suggestions, such as better Kconfig help msg and so on.
Since v2:
- Don't set "-mstrict-align" CFLAGS if HAVE_EFFICIENT_UNALIGNED_ACCESS
- collect Reviewed-by tag
Since v1:
- fix typo in commit msg
- fix build error if NOMMU
Jisheng Zhang (2):
riscv: introduce RISCV_EFFICIENT_UNALIGNED_ACCESS
riscv: select DCACHE_WORD_ACCESS for efficient unaligned access HW
arch/riscv/Kconfig | 14 +++++++++++
arch/riscv/Makefile | 2 ++
arch/riscv/include/asm/asm-extable.h | 15 ++++++++++++
arch/riscv/include/asm/word-at-a-time.h | 27 +++++++++++++++++++++
arch/riscv/mm/extable.c | 31 +++++++++++++++++++++++++
5 files changed, 89 insertions(+)
--
2.40.0
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next reply other threads:[~2023-12-25 4:55 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-12-25 4:42 Jisheng Zhang [this message]
2023-12-25 4:42 ` [PATCH v4 1/2] riscv: introduce RISCV_EFFICIENT_UNALIGNED_ACCESS Jisheng Zhang
2023-12-27 4:22 ` Eric Biggers
2023-12-27 10:41 ` David Laight
2023-12-25 4:42 ` [PATCH v4 2/2] riscv: select DCACHE_WORD_ACCESS for efficient unaligned access HW Jisheng Zhang
2024-01-11 14:50 ` [PATCH v4 0/2] riscv: enable EFFICIENT_UNALIGNED_ACCESS and DCACHE_WORD_ACCESS patchwork-bot+linux-riscv
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