From: Ingo Molnar <mingo@kernel.org>
To: Uros Bizjak <ubizjak@gmail.com>
Cc: x86@kernel.org, linux-kernel@vger.kernel.org,
Andy Lutomirski <luto@kernel.org>, Nadav Amit <namit@vmware.com>,
Brian Gerst <brgerst@gmail.com>,
Denys Vlasenko <dvlasenk@redhat.com>,
"H . Peter Anvin" <hpa@zytor.com>,
Linus Torvalds <torvalds@linux-foundation.org>,
Peter Zijlstra <peterz@infradead.org>,
Thomas Gleixner <tglx@linutronix.de>,
Borislav Petkov <bp@alien8.de>,
Josh Poimboeuf <jpoimboe@redhat.com>
Subject: Re: [PATCH 4/4] x86/percpu: Use C for percpu read/write accessors
Date: Wed, 4 Oct 2023 18:37:52 +0200 [thread overview]
Message-ID: <ZR2U4DLycLT5xFH6@gmail.com> (raw)
In-Reply-To: <20231004145137.86537-5-ubizjak@gmail.com>
* Uros Bizjak <ubizjak@gmail.com> wrote:
> The percpu code mostly uses inline assembly. Using segment qualifiers
> allows to use C code instead, which enables the compiler to perform
> various optimizations (e.g. propagation of memory arguments). Convert
> percpu read and write accessors to C code, so the memory argument can
> be propagated to the instruction that uses this argument.
>
> Some examples of propagations:
>
> a) into sign/zero extensions:
>
> 110b54: 65 0f b6 05 00 00 00 movzbl %gs:0x0(%rip),%eax
> 11ab90: 65 0f b6 15 00 00 00 movzbl %gs:0x0(%rip),%edx
> 14484a: 65 0f b7 35 00 00 00 movzwl %gs:0x0(%rip),%esi
> 1a08a9: 65 0f b6 43 78 movzbl %gs:0x78(%rbx),%eax
> 1a08f9: 65 0f b6 43 78 movzbl %gs:0x78(%rbx),%eax
>
> 4ab29a: 65 48 63 15 00 00 00 movslq %gs:0x0(%rip),%rdx
> 4be128: 65 4c 63 25 00 00 00 movslq %gs:0x0(%rip),%r12
> 547468: 65 48 63 1f movslq %gs:(%rdi),%rbx
> 5474e7: 65 48 63 0a movslq %gs:(%rdx),%rcx
> 54d05d: 65 48 63 0d 00 00 00 movslq %gs:0x0(%rip),%rcx
Could you please also quote a 'before' assembly sequence, at least once
per group of propagations?
Ie. readers will be able to see what kind of code generation changes
result in this kind of text size reduction:
> text data bss dec hex filename
> 25508862 4386540 808388 30703790 1d480ae vmlinux-vanilla.o
> 25500922 4386532 808388 30695842 1d461a2 vmlinux-new.o
Thanks,
Ingo
next prev parent reply other threads:[~2023-10-04 16:38 UTC|newest]
Thread overview: 37+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-10-04 14:49 [PATCH 0/4] x86/percpu: Use segment qualifiers Uros Bizjak
2023-10-04 14:49 ` [PATCH 1/4] x86/percpu: Update arch/x86/include/asm/percpu.h to the current tip Uros Bizjak
2023-10-04 14:49 ` [PATCH 2/4] x86/percpu: Enable named address spaces with known compiler version Uros Bizjak
2023-10-05 7:20 ` [tip: x86/percpu] " tip-bot2 for Uros Bizjak
2023-10-04 14:49 ` [PATCH 3/4] x86/percpu: Use compiler segment prefix qualifier Uros Bizjak
2023-10-05 7:20 ` [tip: x86/percpu] " tip-bot2 for Nadav Amit
2023-10-04 14:49 ` [PATCH 4/4] x86/percpu: Use C for percpu read/write accessors Uros Bizjak
2023-10-04 16:37 ` Ingo Molnar [this message]
2023-10-04 16:40 ` Ingo Molnar
2023-10-04 19:23 ` [PATCH v2 " Uros Bizjak
2023-10-04 19:42 ` Linus Torvalds
2023-10-04 20:07 ` Uros Bizjak
2023-10-04 20:12 ` Linus Torvalds
2023-10-04 20:19 ` Linus Torvalds
2023-10-04 20:22 ` Uros Bizjak
2023-10-05 7:06 ` Ingo Molnar
2023-10-05 7:40 ` Uros Bizjak
2023-10-05 7:20 ` [tip: x86/percpu] " tip-bot2 for Uros Bizjak
2023-10-08 17:59 ` [PATCH 4/4] " Linus Torvalds
2023-10-08 19:17 ` Uros Bizjak
2023-10-08 20:13 ` Linus Torvalds
2023-10-08 20:48 ` Linus Torvalds
2023-10-08 21:41 ` Uros Bizjak
2023-10-09 11:41 ` Ingo Molnar
2023-10-09 11:51 ` Ingo Molnar
2023-10-09 12:00 ` Uros Bizjak
2023-10-09 12:20 ` Ingo Molnar
2023-10-09 12:21 ` Nadav Amit
2023-10-09 12:42 ` Uros Bizjak
2023-10-09 12:53 ` Nadav Amit
2023-10-09 12:27 ` Uros Bizjak
2023-10-09 14:35 ` Uros Bizjak
2024-04-10 11:11 ` Andrey Konovalov
2024-04-10 11:21 ` Uros Bizjak
2024-04-10 11:24 ` Andrey Konovalov
2023-10-09 11:42 ` Ingo Molnar
2023-10-10 6:37 ` Uros Bizjak
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