linux-kernel - perf complains losting events

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Date:	Wed, 3 Aug 2011 18:28:59 +0800
From:	Han Pingtian <phan@...hat.com>
To:	linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>, jolsa@...hat.com
Subject: perf complains losting events

Hi,

I find there is a comment about losting events:

/*
 * The kernel collects the number of events it couldn't send in a stretch and
 * when possible sends this number in a PERF_RECORD_LOST event. The number of
 * such "chunks" of lost events is stored in .nr_events[PERF_EVENT_LOST] while
 * total_lost tells exactly how many events the kernel in fact lost, i.e. it is
 * the sum of all struct lost_event.lost fields reported.
 *
 * The total_period is needed because by default auto-freq is used, so
 * multipling nr_events[PERF_EVENT_SAMPLE] by a frequency isn't possible to get
 * the total number of low level events, it is necessary to to sum all struct
 * sample_event.period and stash the result in total_period.
 */

So my question is, whether the losting of events is a problem? 
I have saw it many times:

[root@...dl580g7-01 perf]# ./perf kmem record sleep 1
[ perf record: Woken up 0 times to write data ]
[ perf record: Captured and wrote 21.789 MB perf.data (~951977 samples)
]
Processed 0 events and LOST 76148!

Check IO/CPU overload!

[root@...dl580g7-01 perf]# ./perf kmem stat
Processed 0 events and LOST 76148!

Check IO/CPU overload!

SUMMARY
=======
Total bytes requested: 5725028
Total bytes allocated: 6291512
Total bytes wasted on internal fragmentation: 566484
Internal fragmentation: 9.003941%
Cross CPU allocations: 28/84295

-- 
Han Pingtian
Quality Engineer
hpt @ #kernel-qe
Red Hat, Inc
Freedom ... courage ... Commitment ... ACCOUNTABILITY
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