From: Peter Zijlstra <peterz@infradead.org>
To: mark.barnett@arm.com
Cc: mingo@redhat.com, acme@kernel.org, namhyung@kernel.org,
irogers@google.com, ben.gainey@arm.com, deepak.surti@arm.com,
ak@linux.intel.com, will@kernel.org, james.clark@arm.com,
mark.rutland@arm.com, alexander.shishkin@linux.intel.com,
jolsa@kernel.org, adrian.hunter@intel.com,
linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v3 3/5] perf: Allow adding fixed random jitter to the alternate sampling period
Date: Mon, 10 Mar 2025 13:47:35 +0100 [thread overview]
Message-ID: <20250310124735.GR5880@noisy.programming.kicks-ass.net> (raw)
In-Reply-To: <20250307202247.648633-4-mark.barnett@arm.com>
On Fri, Mar 07, 2025 at 08:22:45PM +0000, mark.barnett@arm.com wrote:
> @@ -9922,7 +9923,10 @@ static int __perf_event_overflow(struct perf_event *event,
> if (event->attr.alt_sample_period) {
> bool using_alt = hwc->using_alt_sample_period;
> u64 sample_period = (using_alt ? event->attr.sample_period
> - : event->attr.alt_sample_period);
> + : event->attr.alt_sample_period)
> + + (event->attr.jitter_alt_period
> + ? get_random_u32_below(2 << event->attr.jitter_alt_period)
> + : 0);
So, ... this here is NMI context, right? Have you looked at the guts of
get_random_u32_below() ?
I would strongly suggest you go do so.
>
> hwc->sample_period = sample_period;
> hwc->using_alt_sample_period = !using_alt;
next prev parent reply other threads:[~2025-03-10 13:50 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-03-07 20:22 [PATCH v3 0/5] A mechanism for efficient support for per-function metrics mark.barnett
2025-03-07 20:22 ` [PATCH v3 1/5] perf: Record sample last_period before updating mark.barnett
2025-03-07 20:22 ` [PATCH v3 2/5] perf: Allow periodic events to alternate between two sample periods mark.barnett
2025-03-10 12:44 ` Peter Zijlstra
2025-03-07 20:22 ` [PATCH v3 3/5] perf: Allow adding fixed random jitter to the alternate sampling period mark.barnett
2025-03-10 12:47 ` Peter Zijlstra [this message]
2025-03-10 16:27 ` Mark Barnett
2025-03-11 11:31 ` Peter Zijlstra
2025-03-11 11:35 ` Peter Zijlstra
2025-03-12 10:44 ` Peter Zijlstra
2025-03-11 11:37 ` Peter Zijlstra
2025-03-11 17:22 ` Mark Barnett
2025-03-12 9:39 ` Peter Zijlstra
2025-03-07 20:22 ` [PATCH v3 4/5] tools/perf: Modify event parser to support alt-period term mark.barnett
2025-03-07 20:22 ` [PATCH v3 5/5] tools/perf: Modify event parser to support alt-period-jitter term mark.barnett
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