From: Robin Murphy Date: Mon, 23 Jan 2023 18:30:38 +0000 (+0000) Subject: Partially revert "perf/arm-cmn: Optimise DTC counter accesses" X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=a428eb4b99ab80454f06ad256b25e930fe8a4954;p=linux.git Partially revert "perf/arm-cmn: Optimise DTC counter accesses" 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. Fixes: 4f2c3872dde5 ("perf/arm-cmn: Optimise DTC counter accesses") Reported-by: Ilkka Koskinen Signed-off-by: Robin Murphy Link: https://lore.kernel.org/r/b41bb4ed7283c3d8400ce5cf5e6ec94915e6750f.1674498637.git.robin.murphy@arm.com Signed-off-by: Will Deacon --- diff --git a/drivers/perf/arm-cmn.c b/drivers/perf/arm-cmn.c index b80a9b74662b1..1deb61b22bc76 100644 --- a/drivers/perf/arm-cmn.c +++ b/drivers/perf/arm-cmn.c @@ -1576,7 +1576,6 @@ static int arm_cmn_event_init(struct perf_event *event) hw->dn++; continue; } - hw->dtcs_used |= arm_cmn_node_to_xp(cmn, dn)->dtc; hw->num_dns++; if (bynodeid) break; @@ -1589,6 +1588,12 @@ static int arm_cmn_event_init(struct perf_event *event) nodeid, nid.x, nid.y, nid.port, nid.dev, type); return -EINVAL; } + /* + * Keep assuming non-cycles events count in all DTC domains; turns out + * it's hard to make a worthwhile optimisation around this, short of + * going all-in with domain-local counter allocation as well. + */ + hw->dtcs_used = (1U << cmn->num_dtcs) - 1; return arm_cmn_validate_group(cmn, event); }