From: Mark Brown <broonie@kernel.org>
To: Will Deacon <will@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>,
Benjamin Herrenschmidt <benh@kernel.crashing.org>,
linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] arm64/fpsimd: Suppress SVE access traps when loading FPSIMD state
Date: Mon, 21 Aug 2023 13:46:18 +0100 [thread overview]
Message-ID: <12a8953b-2182-43a6-8b4e-6026aa83bf4d@sirena.org.uk> (raw)
In-Reply-To: <20230821121049.GA19670@willie-the-truck>
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On Mon, Aug 21, 2023 at 01:10:50PM +0100, Will Deacon wrote:
> On Mon, Aug 07, 2023 at 11:20:38PM +0100, Mark Brown wrote:
> > I did some instrumentation which counted the number of SVE access traps
> > and the number of times we loaded FPSIMD only register state for each task.
> > Testing with Debian Bookworm this showed that during boot the overwhelming
> > majority of tasks triggered another SVE access trap more than 50% of the
> > time after loading FPSIMD only state with a substantial number near 100%,
> > though some programs had a very small number of SVE accesses most likely
> > from startup. There were few tasks in the range 5-45%, most tasks either
> Do you have any performance numbers to motivate this change? It would be
> interesting, for example, to see how changing the timeout value affects
> the results for some real workloads.
I agree, unfortunately I don't yet have a hardware setup so I can't do
those benchmarks myself at the minute - I just have the access trap
counting I mentioned in the commit message. Last time I saw numbers the
access traps were about 70% of a syscall in a microbenchmark and we're
already suppressing them for non-blocking syscalls so I'd not expect
anything *too* revolutionary.
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prev parent reply other threads:[~2023-08-21 12:46 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-08-07 22:20 [PATCH] arm64/fpsimd: Suppress SVE access traps when loading FPSIMD state Mark Brown
2023-08-21 12:10 ` Will Deacon
2023-08-21 12:46 ` Mark Brown [this message]
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