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([2602:47:d490:6901:9454:a46f:1c22:a7c6]) by smtp.gmail.com with ESMTPSA id w29-20020a63935d000000b0055bf13811f5sm2627789pgm.15.2023.08.05.10.29.13 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sat, 05 Aug 2023 10:29:14 -0700 (PDT) Message-ID: <53a2d13f-b508-0dba-5f0a-1b158372d1a4@linaro.org> Date: Sat, 5 Aug 2023 10:29:12 -0700 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.13.0 Subject: Re: [RFC][PATCH] Reduce generated code by 3% by increasing MMU indices Content-Language: en-US To: Helge Deller , qemu-devel@nongnu.org References: From: Richard Henderson In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=2607:f8b0:4864:20::62e; envelope-from=richard.henderson@linaro.org; helo=mail-pl1-x62e.google.com X-Spam_score_int: -21 X-Spam_score: -2.2 X-Spam_bar: -- X-Spam_report: (-2.2 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-0.089, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On 8/5/23 09:47, Helge Deller wrote: > Do we want to enable such an performance optimization? > If so, I see two possibilities: > > a) Re-define NB_MMU_MODES per target No, we've just gotten rid of per target definitions of NB_MMU_MODES, on the way to being able to support multiple targets simultaneously. This only affects x86, and for only 6 bytes per memory access. While saving code size is a nice goal, I sincerely doubt you can measure any performance difference. If there were a way to change no more than two lines of code, that would be fine. But otherwise I don't see this as being worth making the rest of the code base any more complex. r~