• Kirill Smelkov's avatar
    perf record: Add "nodelay" mode, disabled by default · acac03fa
    Kirill Smelkov authored
    Sometimes there is a need to use perf in "live-log" mode. The problem
    is, for seldom events, actual info output is largely delayed because
    perf-record reads sample data in whole pages.
    
    So for such scenarious, add flag for perf-record to go in "nodelay"
    mode. To track e.g. what's going on in icmp_rcv while ping is running
    Use it with something like this:
    
    (1) $ perf probe -L icmp_rcv | grep -U8 '^ *43\>'
                                        goto error;
                        }
             38         if (!pskb_pull(skb, sizeof(*icmph)))
                                goto error;
                        icmph = icmp_hdr(skb);
    
             43         ICMPMSGIN_INC_STATS_BH(net, icmph->type);
                        /*
                         *      18 is the highest 'known' ICMP type. Anything else is a mystery
                         *
                         *      RFC 1122: 3.2.2  Unknown ICMP messages types MUST be silently
                         *                discarded.
                         */
             50         if (icmph->type > NR_ICMP_TYPES)
                                goto error;
    
        $ perf probe icmp_rcv:43 'type=icmph->type'
    
    (2) $ cat trace-icmp.py
        [...]
        def trace_begin():
                print "in trace_begin"
    
        def trace_end():
                print "in trace_end"
    
        def probe__icmp_rcv(event_name, context, common_cpu,
                common_secs, common_nsecs, common_pid, common_comm,
                __probe_ip, type):
                        print_header(event_name, common_cpu, common_secs, common_nsecs,
                                common_pid, common_comm)
    
                        print "__probe_ip=%u, type=%u\n" % \
                        (__probe_ip, type),
        [...]
    
    (3) $ perf record -a -D -e probe:icmp_rcv -o - | \
          perf script -i - -s trace-icmp.py
    
    Thanks to Peter Zijlstra for pointing how to do it.
    
    Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
    Cc: Frederic Weisbecker <fweisbec@gmail.com>
    Cc: Ingo Molnar <mingo@elte.hu>, Mike Galbraith <efault@gmx.de>
    Cc: Paul Mackerras <paulus@samba.org>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Stephane Eranian <eranian@google.com>
    Cc: Tom Zanussi <tzanussi@gmail.com>
    LKML-Reference: <20110112140613.GA11698@tugrik.mns.mnsspb.ru>
    Signed-off-by: default avatarKirill Smelkov <kirr@mns.spb.ru>
    Signed-off-by: default avatarArnaldo Carvalho de Melo <acme@redhat.com>
    acac03fa
perf-record.txt 2.96 KB