Messages in this thread | | | Date | Mon, 21 Aug 2023 13:46:18 +0100 | From | Mark Brown <> | Subject | Re: [PATCH] arm64/fpsimd: Suppress SVE access traps when loading FPSIMD state |
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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. [unhandled content-type:application/pgp-signature] | |