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[216.180.64.156]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-2ee0fad03c7sm3944850a91.39.2024.11.28.13.38.47 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 28 Nov 2024 13:38:47 -0800 (PST) From: Pierrick Bouvier To: qemu-devel@nongnu.org Cc: Richard Henderson , =?utf-8?q?Alex_Benn?= =?utf-8?q?=C3=A9e?= , Paolo Bonzini , Alexandre Iooss , Mahmoud Mandour , Pierrick Bouvier Subject: [PATCH v2] plugins: optimize cpu_index code generation Date: Thu, 28 Nov 2024 13:38:43 -0800 Message-Id: <20241128213843.1023080-1-pierrick.bouvier@linaro.org> X-Mailer: git-send-email 2.39.5 MIME-Version: 1.0 Received-SPF: pass client-ip=2607:f8b0:4864:20::433; envelope-from=pierrick.bouvier@linaro.org; helo=mail-pf1-x433.google.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 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, 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 When running with a single vcpu, we can return a constant instead of a load when accessing cpu_index. A side effect is that all tcg operations using it are optimized, most notably scoreboard access. When running a simple loop in user-mode, the speedup is around 20%. Signed-off-by: Pierrick Bouvier Reviewed-by: Richard Henderson --- v2: - no need to do a flush, as user-mode already does it when spawning a second cpu (to honor CF_PARALLEL flags). - change condition detection to use CF_PARALLEL instead --- accel/tcg/plugin-gen.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/accel/tcg/plugin-gen.c b/accel/tcg/plugin-gen.c index 0f47bfbb489..961d9305913 100644 --- a/accel/tcg/plugin-gen.c +++ b/accel/tcg/plugin-gen.c @@ -102,6 +102,15 @@ static void gen_disable_mem_helper(void) static TCGv_i32 gen_cpu_index(void) { + /* + * Optimize when we run with a single vcpu. All values using cpu_index, + * including scoreboard index, will be optimized out. + * User-mode calls tb_flush when setting this flag. In system-mode, all + * vcpus are created before generating code. + */ + if (!tcg_cflags_has(current_cpu, CF_PARALLEL)) { + return tcg_constant_i32(current_cpu->cpu_index); + } TCGv_i32 cpu_index = tcg_temp_ebb_new_i32(); tcg_gen_ld_i32(cpu_index, tcg_env, -offsetof(ArchCPU, env) + offsetof(CPUState, cpu_index));