linux-kernel - Re: [PATCH v10 09/12] perf record: implement -z,--compression

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Date:   Wed, 15 May 2019 18:44:29 +0300
From:   Alexey Budankov <alexey.budankov@...ux.intel.com>
To:     Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>
Cc:     Jiri Olsa <jolsa@...hat.com>, Namhyung Kim <namhyung@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Andi Kleen <ak@...ux.intel.com>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v10 09/12] perf record: implement
 -z,--compression_level[=<n>] option

On 15.05.2019 15:59, Arnaldo Carvalho de Melo wrote:
> Em Wed, May 15, 2019 at 11:43:30AM +0300, Alexey Budankov escreveu:
>> On 15.05.2019 0:46, Arnaldo Carvalho de Melo wrote:
>>> Em Tue, May 14, 2019 at 05:20:41PM -0300, Arnaldo Carvalho de Melo escreveu:
>>>> Em Mon, Mar 18, 2019 at 08:44:42PM +0300, Alexey Budankov escreveu:
> 
>>>>> Implemented -z,--compression_level[=<n>] option that enables compression
>>>>> of mmaped kernel data buffers content in runtime during perf record
>>>>> mode collection. Default option value is 1 (fastest compression).
> 
>>> <SNIP>
> 
>>>> [root@...co ~]# perf record -z2
>>>> ^C[ perf record: Woken up 1 times to write data ]
>>>> 0x1746e0 [0x76]: failed to process type: 81 [Invalid argument]
>>>> [ perf record: Captured and wrote 1.568 MB perf.data, compressed (original 0.452 MB, ratio is 3.995) ]
> 
>>>> [root@...co ~]#
> 
>>> So, its the buildid processing at the end, so we can't do build-id
>>> processing when using PERF_RECORD_COMPRESSED, otherwise we'd have to
>>> uncompress at the end to find the PERF_RECORD_FORK/PERF_RECORD_MMAP,
>>> etc.
> 
>>> [root@...co ~]# perf record -z2  --no-buildid sleep 1
>>> [ perf record: Woken up 1 times to write data ]
>>> [ perf record: Captured and wrote 0.020 MB perf.data, compressed (original 0.001 MB, ratio is 2.153) ]
>>> [root@...co ~]# perf report -D | grep PERF_RECORD_COMP
>>> 0x4f40 [0x195]: failed to process type: 81 [Invalid argument]
>>> Error:
>>> failed to process sample
>>> 0 0x4f40 [0x195]: PERF_RECORD_COMPRESSED
>>> [root@...co ~]#
> 
>>> I'll play with it tomorrow.
> 
>> Applied the whole patch set on top of the current perf/core 
>> and the whole thing functions as expected.
> 
> It doesn't, see the reported error above, these three lines, that
> shouldn't be there:
> 
> 0x4f40 [0x195]: failed to process type: 81 [Invalid argument]
> Error:
> failed to process sample
> 
> That is because at this point in the patch series a record was
> introduced that is not being handled by the build id processing done, by
> default, at the end of the 'perf record' session, and, as explained
> above, needs fixing so that when we do 'git bisect' looking for a non
> expected "failed to process type: 81" kind of error, this doesn't
> appear.
> 
> I added the changes below to this cset and will continue from there:
> 
> diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
> index d84a4885e341..f8d21991f94c 100644
> --- a/tools/perf/builtin-record.c
> +++ b/tools/perf/builtin-record.c
> @@ -2284,6 +2284,12 @@ int cmd_record(int argc, const char **argv)
>  			"cgroup monitoring only available in system-wide mode");
>  
>  	}
> +
> +	if (rec->opts.comp_level != 0) {
> +		pr_debug("Compression enabled, disabling build id collection at the end of the session\n");
> +		rec->no_buildid = true;
> +	}
> +
>  	if (rec->opts.record_switch_events &&
>  	    !perf_can_record_switch_events()) {
>  		ui__error("kernel does not support recording context switch events\n");
> 
> ---------------------------------------------------------------------------
> 
> [acme@...co perf]$ perf record -z2 sleep 1
> [ perf record: Woken up 1 times to write data ]
> [ perf record: Captured and wrote 0.001 MB perf.data, compressed (original 0.001 MB, ratio is 2.292) ]
> [acme@...co perf]$ perf record -v -z2 sleep 1
> Compression enabled, disabling build id collection at the end of the session
> Using CPUID GenuineIntel-6-8E-A
> nr_cblocks: 0
> affinity: SYS
> mmap flush: 1
> comp level: 2
> mmap size 528384B
> Couldn't start the BPF side band thread:
> BPF programs starting from now on won't be annotatable
> perf_event__synthesize_bpf_events: can't get next program: Operation not permitted
> [ perf record: Woken up 1 times to write data ]
> [ perf record: Captured and wrote 0.001 MB perf.data, compressed (original 0.001 MB, ratio is 2.305) ]
> [acme@...co perf]$
> 
> Will check if its possible to get rid of the following in this patch, to
> keep bisection working for this case as well:
> 
> [acme@...co perf]$ perf report -D | grep COMPRESS
> 0x1b8 [0x169]: failed to process type: 81 [Invalid argument]
> Error:
> failed to process sample
> 0 0x1b8 [0x169]: PERF_RECORD_COMPRESSED
> [acme@...co perf]$

Makes sense. Thanks.

~Alexey

> 
> - Arnaldo
>