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McKenney" , Boqun Feng , Paolo Bonzini , Sean Christopherson , Wei Liu , Dexuan Cui , x86@kernel.org, Arnd Bergmann , Heiko Carstens , Christian Borntraeger , Sven Schnelle , Huacai Chen , Paul Walmsley , Palmer Dabbelt References: <20250908212737.353775467@linutronix.de> <4029c2d2-7a0c-4531-aa1e-b35be9098bb1@kernel.dk> From: Michael Jeanson Content-Language: fr Autocrypt: addr=mjeanson@efficios.com; keydata= xsFNBE0j2GkBEACcli1fPgaQ/9lCQA8xCtMmGARVfTzhyIstl41wnBdEijU6RN3EzzPc8j1i fsdK6DBEWLEoQBkFZLPmq+HJ1sNsUsJRe9OzYuetcSvDRPu8XEsLkO8akmC3fo5/Pk6iLnRb +Ge0nsNii5CSULPnHUgCxyBGcKm8hWqB4m/t79MOXHDAHNQt6ecP0ss86/vLMXpzLg9yyXBu sY1HrHMbUNssE0kqMgEmoq3v6JRwK9Qv1WDmNzl3UgMd2WZKUv0sQjyOCh/13R8Clk8Ljjnc n/RrHp6XIWreXZRTU0cL9ZfFjTntci82Je5pKWiLSaNAIHKFo8AMwvum52SqSxA76YkcNyGk 9S8O3A6tQAhZkl4rn2eF3qd1I33G+8gyvFuL8omP566rJ0PnF2hDP5FqKcbpUjs6eMWLqPYD 6AirkGurX1FmA7gg6MAiOuLptcGPYslavQK6gmcYtnjVYfueEpBzj/6jl0b3gpVYmGd/e52f mU6krF0By/Ch0Nmk3YDPuhEig4jWXmvov0BTcVFKdS7Axxh8pdZYcgz87gBgsqr90Rg7ioLB ldgI/698cXNlBWGWRvxshbEXidQF3dgksTafWylLYQVCPCHXYcVXkpoHfsEBKYKTIezT7CCA EvSDlN4X+ncIzRg5CeS3bzs4HrusiOdOjaSkVdifwQxzhvn4RQARAQABzSdNaWNoYWVsIEpl YW5zb24gPG1qZWFuc29uQGVmZmljaW9zLmNvbT7CwZQEEwEKAD4CGwMFCwkIBwMFFQoJCAsF FgIDAQACHgECF4AWIQSYZiQyQrZCJ3niC2KGVh9FIYD8/gUCZ//KEgUJHeiBpwAKCRCGVh9F IYD8/mhQD/wOShaTLm2UjDz1VwDM5l0gxfnwqG/xc69G+eDsXQoL+Ad2kc4cTKGXnkFxW/hN QMZ9dG3LeD1oqfIYSQaUC3OUZPSE07r6kH4UMkFFY6XUhBBONHD/lqGaY7FsvrPSVKo3T3GA Bc7bD/OsSgvWNyKktfxFbzm4SzO7N0ALBMC4qEaaJW68bfM/ID4Sx1gNFUFa88qghjgizfzO +4aHkxQ4MlfZ1nN0UxISlWxKt2YqfPcUdjl+8nDk0je1/6nKA9qXLBB5fbONXBGe1Bm7yiqz AlGIVJpfEKl6r74YdYzNSKuHIOAaHY5BJ5MX/0EyBAp7t6jGvt1WCqO+R3JBZnQ+/F2JFaXc aI1ay4F1ermRxcSWrxJw/XNIKNfFzgWDKceBAz+U0RUjvtDjqlZ60znh3+oAplvzkfddptQe /WDzWsCIxRnaD0aFcIiKxPc7QqkK1W60/UCjoSXDkbN4A/xa0LmiMMFJErpyRagaetQ6F13y 9oVgO7/W9ooiCTI67wymX8hBMyVZ5NttXzuNmx0TWmI29ZoBMUIaitJ8GBZI9Jxs+SpReear B0935ie2oYr3p+Dm+rGLqIbKTIrLr6o6Bc8bV/RYcMa23qXe4n67nKZJv3jU/GL3o9zobguc EoUUWe9NbBDrbi63Dz/gcGWuUSxLgpiP9i8vlGywGz/Jx87BTQRNI9hpARAAqAkuPLkp3WkX Q/aUKgHM9bVA3Qzx1lx7Cmvhpa9Rn435ciJdf0xEmv1xVwYGjsoMgStX9sb1PzBZePsJGbQ1 rW57hTkgvwqGduDPjbgVVjZ4nHYpfPzggTdm+DOpkAUvUVTRNTe4k6B8Pd/BJYu4TrBM2dLh cNakLzg3Q4rI/2AsOCOjPuRVhClILzaEttksG9KzMyFUxwVr1NAkynZLnjSQyGqKAw71DnRT vzmf3lyG1dY/DSwJyEiV8LOd1Gno6c8F6CTuow3c/J7Ttc5+9MDBiQxySwOH2Xp3ROKUtIbj Quw3cjtkTRrRknZm2EbVrB1C+KF9tAeAVNDkqfQrrdwL9Uvn9EjuHhCVsqIN+WvoJFYoIyhl HUy9uQhWQNn5G/9SNQK3BFAmJhgt64CPBIsOu3mpvMQtZHtJ8Hpfub5Uueew/MJlkYGWr1IG DjrAgDWBYSXTvqcvLpt4Yrp3RqRAsOoKKjomcFv5S0ryTQLO/aaZVTKzha41FxIhd+zUg6/r vc6RWKL+ySS1fOeFk+SaY1GeFLMoT9MgUEXHIkISC1xdA5Zri13MBxkcJkd5sZ/0C5Wlgr+f LuuzzcZX9aDiiV4uAdmy5WHVo6Y/l6MtYq+Fbzp0LSU2KemigHIGZT/gL+zDvduDIZjQZeG4 gNxM1wwsycfIYftHMfg8OVEAEQEAAcLBfAQYAQoAJgIbDBYhBJhmJDJCtkIneeILYoZWH0Uh gPz+BQJn/8o/BQkd6IGnAAoJEIZWH0UhgPz+Y3YQAJJaKODzmQMlxJ7kNTOjBo4wemDo6e5d kJ7xhYinLru+G8qJS0m7EsO51o3WtvrsPFV+RyKQrVW/Sl3m9dK/KxCWewW1itu4OKeHd+k5 UUK7xZg7lbmPFeoIaP0JtS96My0SnWRdRVSh+tQlqC4LlNIw3CiRxrCkfPlsoOBzZkTcx8Ta oYez+F0KKSH4SIk/+tgUvCAkb3JCw3kz5LxmV2NpgsvI6R5uuQ7nLtgEA6Q9g+ahICs0g+w+ HqSU1W+o6xrYZuCej1CFn3bqNuuAQGgVlD4wyS9SbXyCD5AZZwqX0V11C60AhInxCqnpn1hP qusWfhXf0BJeRNzKo7TMd3aB1YnsieNQQRopM4S8D2Embe9DtBX0WeUR/fDGjHiPItkFSel9 Gl6aXqDWDdaf1tKr4eQc845/EljpQF1LxHTp4kpGcyT5IqsA+Xom0lRowFimTwrLkHbAU+6P 3rAy/6dOzcikgkVYGln6nSgZsqeLlOyLUEE0+WpSbR4UxaMjvcM8PIx5rX6FuQxJslQ52emr 2XM0IYMuU6/5TMyTaQdS4p2nu2qu99snefOikIUzAxAp+Y5es/Tazwb83VdEGoN6JxzauDeQ upVaTHEZj/GMlMPGw05QXmB8rQz0aWTGpVBZFpmBWHYsk3QVEAOjQbjMfESW/IHw9EMZs/NH IZHa In-Reply-To: <4029c2d2-7a0c-4531-aa1e-b35be9098bb1@kernel.dk> Content-Type: text/plain; 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Since I last looked at the > rseq performance overhead, glibc must have improved a few things. FWIW, > box is running libc 2.41 at the moment. Test box is on debian unstable, > so gets frequent updates. In any case, for one of my usual kernel > overhead runs of checking running a basic IOPS based test, I see the > following on the stock (-rc5 + 6.18 targeted changes) kernel running > that test: > > + 0.89% io_uring [kernel.kallsyms] [k] __get_user_8 > + 0.58% io_uring [kernel.kallsyms] [k] __put_user_8 > + 1.13% io_uring [kernel.kallsyms] [k] __rseq_handle_notify_resume > > which is about 2.6% of purely rseq related overhead. Pulling in the > above branch and running the exact same test, all of the above are gone > and perusing the profile has nothing jump out at me in terms of shifting > those cycles to other bookkeeping. > > So yes, this work does make a very noticeable difference! If you have time, could you also run the same test on this branch with glibc rseq registration disabled, just to see of there is some noticable differences. To disable glibc automatic registration, just export this variable: GLIBC_TUNABLES="glibc.pthread.rseq=0" Thanks!