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Tue, 23 Sep 2025 00:10:30 -0700 (PDT) X-Google-Smtp-Source: AGHT+IEYOHc3MDHr+TEeYcICfcjGVqjEAvxLcPdHLHqRCHmS3kzA4yXc/Vb6To875f84F7VshkKC1A== X-Received: by 2002:a05:6402:1d24:b0:634:5722:cc3f with SMTP id 4fb4d7f45d1cf-6346779876dmr1131101a12.16.1758611430130; Tue, 23 Sep 2025 00:10:30 -0700 (PDT) Received: from [192.168.10.48] ([176.206.127.188]) by smtp.googlemail.com with ESMTPSA id 4fb4d7f45d1cf-62fa5f2b4d3sm10309499a12.42.2025.09.23.00.10.29 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 23 Sep 2025 00:10:29 -0700 (PDT) Message-ID: <67f2c84b-4bb3-437b-8184-e7dfb9947df9@redhat.com> Date: Tue, 23 Sep 2025 09:10:28 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 09/12] accel/tcg: Introduce EXCP_TB_FLUSH To: Richard Henderson , qemu-devel@nongnu.org References: <20250923023922.3102471-1-richard.henderson@linaro.org> <20250923023922.3102471-10-richard.henderson@linaro.org> From: Paolo Bonzini Content-Language: en-US Autocrypt: addr=pbonzini@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=170.10.129.124; envelope-from=pbonzini@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -24 X-Spam_score: -2.5 X-Spam_bar: -- X-Spam_report: (-2.5 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.442, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, RCVD_IN_VALIDITY_CERTIFIED_BLOCKED=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, SPF_HELO_PASS=-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 9/23/25 04:39, Richard Henderson wrote: > We are going to disallow tb_flush from within the context > of a running cpu. Introduce a tcg-internal exception to > return out of the cpu run loop and perform the flush there. > > Signed-off-by: Richard Henderson One small difference is that different CPUs can fail tcg_tb_alloc() at the same time and flush multiple times. I think the check on the generation count should remain. Instead of introducing EXCP_TB_FLUSH, you can keep the guts of tb_flush() as void tb_queue_flush(CPUState *cpu) { unsigned tb_flush_count = qatomic_read(&tb_ctx.tb_flush_count); async_safe_run_on_cpu(cpu, do_tb_flush, RUN_ON_CPU_HOST_INT(tb_flush_count)); } With the unconditional async_safe_run_on_cpu() hidden behind a function, this patch goes away while the next one survives as if (unlikely(!tb)) { - /* flush must be done */ - tb_flush(cpu); mmap_unlock(); - /* Make the execution loop process the flush as soon as possible. */ - cpu->exception_index = EXCP_INTERRUPT; + tb_queue_flush(cpu); cpu_loop_exit(cpu); } Paolo