Re: sve_user_discard
flat view
From: Catalin Marinas <catalin.marinas@arm.com>
Date: 2021-05-21 09:13:05
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On Thu, May 20, 2021 at 04:02:03PM -0700, psodagud@codeaurora.org wrote:
This is regarding sve_user_disable(CPACR_EL1_ZEN_EL0EN) on every system call. If a userspace task is using SVE instructions and making sys calls in between, it would impact the performance of the thread. On every SVE instructions after SVC/system call, it would trap to EL1. I think by setting CPACR_EL1_ZEN_EL0EN flag, the processor faults when it runs an SVE instruction. This approach may be taken as part of FPSIMD registers switching optimizations. Can below portion of the code use thread.fpsimd_cpu and fpsimd_last_state variables to avoid clearing CPACR_EL1_ZEN_EL0EN for this kind of use cases?
There were attempts over the past couple of years to optimise the syscall return use-case. I think the latest is this one: https://lore.kernel.org/r/20201106193553.22946-2-broonie@kernel.org (local) I'll let Mark comment on his plans for reviving the series. Do you happen to have some realistic workload that would be improved by this? We can always write a micro-benchmark but I wonder how much this matters in the real world. -- Catalin _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel