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[67.174.166.185]) by smtp.gmail.com with ESMTPSA id p12sm3298438qkj.54.2021.10.01.09.42.01 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 01 Oct 2021 09:42:02 -0700 (PDT) Subject: Re: [RFC PATCH 00/13] x86 User Interrupts support To: Stefan Hajnoczi , Sohil Mehta , Peter Maydell , =?UTF-8?Q?Alex_Benn=c3=a9e?= References: <20210913200132.3396598-1-sohil.mehta@intel.com> <456bf9cf-87b8-4c3d-ac0c-7e392bcf26de@www.fastmail.com> <778d40fe-ad8e-fd7c-4caa-499910bb0925@intel.com> From: Richard Henderson Message-ID: <3abdadab-9b7e-7cc0-5ec5-17fa385ce7d4@linaro.org> Date: Fri, 1 Oct 2021 12:41:59 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.13.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=2607:f8b0:4864:20::731; envelope-from=richard.henderson@linaro.org; helo=mail-qk1-x731.google.com X-Spam_score_int: -31 X-Spam_score: -3.2 X-Spam_bar: --- X-Spam_report: (-3.2 / 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=-1.127, 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: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: "Peter Zijlstra \(Intel\)" , qemu-devel@nongnu.org, Dave Hansen , linux-kselftest@vger.kernel.org, "H. Peter Anvin" , Shuah Khan , Thomas Gleixner , linux-arch@vger.kernel.org, Raj Ashok , Jonathan Corbet , the arch/x86 maintainers , Ingo Molnar , Zeng Guang , Gayatri Kammela , "Shankar, Ravi V" , Jacob Pan , Arnd Bergmann , Ramesh Thomas , Borislav Petkov , Andy Lutomirski , "Williams, Dan J" , Christian Brauner , Jens Axboe , Tony Luck , Linux API , Randy E Witt , Linux Kernel Mailing List Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 10/1/21 12:35 PM, Stefan Hajnoczi wrote: > QEMU's TCG threads execute translated code. There are events that > require interrupting these threads. Today a check is performed at the > start of every translated block. Most of the time the check is false and > it's a waste of CPU. > > User interrupts can eliminate the need for checks by interrupting TCG > threads when events occur. We used to use interrupts, and stopped because we need to wait until the guest is in a stable state. The guest is always in a stable state at the beginning of each TB. See 378df4b2375. r~