From: Peter Zijlstra <peterz@infradead.org>
To: Andi Kleen <andi@firstfloor.org>
Cc: acme@kernel.org, jolsa@kernel.org, eranian@google.com,
linux-kernel@vger.kernel.org, mingo@kernel.org,
Andi Kleen <ak@linux.intel.com>
Subject: Re: [PATCH 09/11] x86, perf: Support sysfs files depending on SMT status
Date: Mon, 18 Jan 2016 19:06:14 +0100 [thread overview]
Message-ID: <20160118180614.GV6357@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <1452906773-7581-10-git-send-email-andi@firstfloor.org>
On Fri, Jan 15, 2016 at 05:12:51PM -0800, Andi Kleen wrote:
> +ssize_t events_ht_sysfs_show(struct device *dev, struct device_attribute *attr,
> + char *page)
> +{
> + struct perf_pmu_events_ht_attr *pmu_attr =
> + container_of(attr, struct perf_pmu_events_ht_attr, attr);
> +
> + /*
> + * Report conditional events depending on Hyper-Threading.
> + *
> + * This is overly conservative as usually the HT special
> + * handling is not needed if the other CPU thread is idle.
> + *
> + * Note this does not (cannot) handle the case when thread
> + * siblings are invisible, for example with virtualization
> + * if they are owned by some other guest. The user tool
> + * has to re-read when a thread sibling gets onlined later.
> + */
> +
> + return sprintf(page, "%s",
> + x86_pmu.ht_on ?
> + pmu_attr->event_str_ht :
> + pmu_attr->event_str_noht);
> +}
So one obvious problem with this is that a concurrent hotplug operation
can toggle ht_on resulting in bogus measurements.
I'm not sure there's anything we can do about that, other than WARN in
the tool if it finds inconsistent results; does it?
next prev parent reply other threads:[~2016-01-18 18:06 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-01-16 1:12 Add top down metrics to perf stat Andi Kleen
2016-01-16 1:12 ` [PATCH 01/11] perf, tools: Dont stop PMU parsing on alias parse error Andi Kleen
2016-01-16 1:12 ` [PATCH 02/11] perf, tools: Parse an .aggr-per-core event attribute Andi Kleen
2016-01-16 1:12 ` [PATCH 03/11] perf, tools, stat: Force --per-core mode for .aggr-per-core aliases Andi Kleen
2016-01-16 1:12 ` [PATCH 04/11] perf, tools, stat: Avoid fractional digits for integer scales Andi Kleen
2016-01-16 1:12 ` [PATCH 05/11] perf, tools, stat: Scale values by unit before metrics Andi Kleen
2016-01-16 1:12 ` [PATCH 06/11] perf, tools, stat: Basic support for TopDown in perf stat Andi Kleen
2016-01-16 1:12 ` [PATCH 07/11] perf, tools, stat: Add computation of TopDown formulas Andi Kleen
2016-01-16 1:12 ` [PATCH 08/11] perf, tools, stat: Add extra output of counter values with -v Andi Kleen
2016-01-16 1:12 ` [PATCH 09/11] x86, perf: Support sysfs files depending on SMT status Andi Kleen
2016-01-18 18:03 ` Peter Zijlstra
2016-01-18 18:06 ` Peter Zijlstra [this message]
2016-01-18 22:28 ` Andi Kleen
2016-01-16 1:12 ` [PATCH 10/11] x86, perf: Add Top Down events to Intel Core Andi Kleen
2016-01-16 1:12 ` [PATCH 11/11] x86, perf: Add Top Down events to Intel Atom Andi Kleen
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