Re: [PATCH v2 15/18] perf: arm_spe: Handle guest/host exclusion flags
From: Marc Zyngier <maz@kernel.org>
Date: 2019-12-22 12:10:57
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On Fri, 20 Dec 2019 14:30:22 +0000, Andrew Murray [off-list ref] wrote:
quoted hunk ↗ jump to hunk
A side effect of supporting the SPE in guests is that we prevent the host from collecting data whilst inside a guest thus creating a black-out window. This occurs because instead of emulating the SPE, we share it with our guests. Let's accurately describe our capabilities by using the perf exclude flags to prevent !exclude_guest and exclude_host flags from being used. Signed-off-by: Andrew Murray <redacted> --- drivers/perf/arm_spe_pmu.c | 3 +++ 1 file changed, 3 insertions(+)diff --git a/drivers/perf/arm_spe_pmu.c b/drivers/perf/arm_spe_pmu.c index 2d24af4cfcab..3703dbf459de 100644 --- a/drivers/perf/arm_spe_pmu.c +++ b/drivers/perf/arm_spe_pmu.c@@ -679,6 +679,9 @@ static int arm_spe_pmu_event_init(struct perf_event *event) if (attr->exclude_idle) return -EOPNOTSUPP; + if (!attr->exclude_guest || attr->exclude_host) + return -EOPNOTSUPP; +
I have the opposite approach. If the host decides to profile the guest, why should that be denied? If there is a black hole, it should take place in the guest. Today, the host does expect this to work, and there is no way that we unconditionally allow it to regress. M. -- Jazz is not dead, it just smells funny. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel