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Robin Murphy authored
It turns out the optimisation implemented by commit 4f2c3872 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. Fixes: 4f2c3872 ("perf/arm-cmn: Optimise DTC counter accesses") Reported-by:
Ilkka Koskinen <ilkka@os.amperecomputing.com> Signed-off-by:
Robin Murphy <robin.murphy@arm.com> Link: https://lore.kernel.org/r/b41bb4ed7283c3d8400ce5cf5e6ec94915e6750f.1674498637.git.robin.murphy@arm.comSigned-off-by:
Will Deacon <will@kernel.org>
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