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Date: Fri, 15 Mar 2019 10:06:37 +0000 From: Dave Martin <Dave.Martin@....com> To: Julien Grall <julien.grall@....com> Cc: Sebastian Andrzej Siewior <bigeasy@...utronix.de>, Ard Biesheuvel <ard.biesheuvel@...aro.org>, linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>, linux-rt-users@...r.kernel.org, Catalin Marinas <catalin.marinas@....com>, Will Deacon <will.deacon@....com>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org> Subject: Re: [RFC PATCH] arm64/fpsimd: Don't disable softirq when touching FPSIMD/SVE state On Thu, Mar 14, 2019 at 06:07:19PM +0000, Julien Grall wrote: > Hi Sebastian, > > On 3/4/19 5:25 PM, Sebastian Andrzej Siewior wrote: [...] > >It would increase the softirq latency but the question is how bad would > >it be. It would continue once the SIMD section is done. > > On Arm, the kernel may use either FPSIMD or SVE (if supported by the > platform). While the FPSIMD context is fairly small (~4K), the SVE context > can be up to ~64KB. It's not quite as bad as that. The FPSIMD state is ~0.5K, with the SVE state size being up to ~8.5K (though for today's implementations ~2K may be considered typical). For comparision, I believe AVX-512 has ~2K of state. Cheers ---Dave
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