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Tue, 27 Oct 2026 09:39:35 -0700 (PDT) Received: from localhost ([153.61.198.240]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2eae6c9ea8asm12504955ad.66.2026.10.27.09.39.35 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 27 Oct 2026 09:39:35 -0700 (PDT) Content-Type: text/plain; charset=UTF-8 Date: Tue, 27 Oct 2026 16:39:34 +0000 Message-Id: Cc: , , , Subject: Re: [PATCH bpf 07/81] bpf: One time slice of may_goto for a run of a prog From: "Alexei Starovoitov" To: "Kumar Kartikeya Dwivedi" In-Reply-To: References: <20261026025943.404450-1-alexei.starovoitov@gmail.com> <20261026025943.404450-8-alexei.starovoitov@gmail.com> X-Mailer: mkdraft (claude review draft; edit before sending) Content-Transfer-Encoding: 8bit X-Mailing-List: bpf@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 On Mon, Oct 26, 2026 at 10:35 AM Kumar Kartikeya Dwivedi wrote: >> Limitations: >> - A second run of the same prog on the same cpu, in an interrupt or after >> preemption, starts the time slice again. The timestamp in the frame >> continues to limit each frame to 250 ms. >> - The JIT must support a stack walk and per-cpu insns. x86-64 with ORC, >> arm64 and powerpc64 do. Nothing changes on riscv, loongarch and s390. >> - Nothing changes for extension progs. They cannot find the start of a >> run. [...] > Why not copy the state from the caller's frame into the callee iff it > uses may_goto? At least it will work correctly without various holes > listed here in the limitations. Because of callbacks. The caller of cb is C code. There is no bpf frame to copy from. Direct calls are hard too. Would need some hidden arg to be passed, so that callee knows where to copy from. We've been sitting on this issue for long time. I felt we have to close this hole now and improve later if we can think of a better way.