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[31.46.245.48]) by smtp.gmail.com with ESMTPSA id f11-20020a056402160b00b00532eba07773sm110900edv.25.2023.10.04.09.37.53 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 04 Oct 2023 09:37:54 -0700 (PDT) Sender: Ingo Molnar Date: Wed, 4 Oct 2023 18:37:52 +0200 From: Ingo Molnar To: Uros Bizjak Cc: x86@kernel.org, linux-kernel@vger.kernel.org, Andy Lutomirski , Nadav Amit , Brian Gerst , Denys Vlasenko , "H . Peter Anvin" , Linus Torvalds , Peter Zijlstra , Thomas Gleixner , Borislav Petkov , Josh Poimboeuf Subject: Re: [PATCH 4/4] x86/percpu: Use C for percpu read/write accessors Message-ID: References: <20231004145137.86537-1-ubizjak@gmail.com> <20231004145137.86537-5-ubizjak@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20231004145137.86537-5-ubizjak@gmail.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Uros Bizjak 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