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[174.21.81.121]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-20beeca49ccsm24807595ad.66.2024.10.04.07.34.40 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 04 Oct 2024 07:34:41 -0700 (PDT) Message-ID: <1de09840-4689-47d1-bc26-47f19e050a08@linaro.org> Date: Fri, 4 Oct 2024 07:34:39 -0700 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH] accel/tcg: add tracepoints for cpu_loop_exit_atomic To: =?UTF-8?Q?Alex_Benn=C3=A9e?= , qemu-devel@nongnu.org Cc: Pierrick Bouvier , Paolo Bonzini , Riku Voipio References: <20241004135226.903570-1-alex.bennee@linaro.org> Content-Language: en-US From: Richard Henderson In-Reply-To: <20241004135226.903570-1-alex.bennee@linaro.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit 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: -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 On 10/4/24 06:52, Alex Bennée wrote: > We try to avoid using cpu_loop_exit_atomic as it brings in an all-core > sync point. However on some cpu/kernel/benchmark combinations it is > starting to show up in the performance profile. To make it easier to > see whats going on add tracepoints for the slow path so we can see > what is triggering the wait. > > It seems for a modern CPU it can be quite a bit, for example: > > ./qemu-system-aarch64 \ > -machine type=virt,virtualization=on,pflash0=rom,pflash1=efivars,gic-version=max \ > -smp 4 \ > -accel tcg \ > -device virtio-net-pci,netdev=unet \ > -device virtio-scsi-pci \ > -device scsi-hd,drive=hd \ > -netdev user,id=unet,hostfwd=tcp::2222-:22 \ > -blockdev driver=raw,node-name=hd,file.driver=host_device,file.filename=/dev/zen-ssd2/trixie-arm64,discard=unmap \ > -serialmon:stdio \ > -blockdev node-name=rom,driver=file,filename=(pwd)/pc-bios/edk2-aarch64-code.fd,read-only=true \ > -blockdev node-name=efivars,driver=file,filename=$HOME/images/qemu-arm64-efivars \ > -m 8192 \ > -object memory-backend-memfd,id=mem,size=8G,share=on \ > -kernel /home/alex/lsrc/linux.git/builds/arm64/arch/arm64/boot/Image -append "root=/dev/sda2 console=ttyAMA0 systemd.unit=benchmark-stress-ng.service" \ > -display none -dtrace:load_atom\*_fallback,trace:store_atom\*_fallback > > With: > > -cpu neoverse-v1,pauth-impdef=on => 2203343 > > With: > > -cpu cortex-a76 => 0 > > Signed-off-by: Alex Bennée > Cc: Pierrick Bouvier > --- > accel/tcg/user-exec.c | 2 +- > accel/tcg/ldst_atomicity.c.inc | 9 +++++++++ > accel/tcg/trace-events | 12 ++++++++++++ > 3 files changed, 22 insertions(+), 1 deletion(-) Reviewed-by: Richard Henderson r~