Re: [PATCH] Partially revert "perf/arm-cmn: Optimise DTC counter accesses"

[Will Deacon]

On Mon, 23 Jan 2023 18:30:38 +0000, Robin Murphy wrote:
> It turns out the optimisation implemented by commit 4f2c3872dde5 is
> totally broken, since all the places that consume hw->dtcs_used for
> events other than cycle count are still not expecting it to be sparsely
> populated, and fail to read all the relevant DTC counters correctly if
> so.
> 
> If implemented correctly, the optimisation potentially saves up to 3
> register reads per event update, which is reasonably significant for
> events targeting a single node, but still not worth a massive amount of
> additional code complexity overall. Getting it right within the current
> design looks a fair bit more involved than it was ever intended to be,
> so let's just make a functional revert which restores the old behaviour
> while still backporting easily.
> 
> [...]

Applied to arm64 (for-next/fixes), thanks!

[1/1] Partially revert "perf/arm-cmn: Optimise DTC counter accesses"
      https://git.kernel.org/arm64/c/a428eb4b99ab

Cheers,
-- 
Will

https://fixes.arm64.dev
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