linux-kernel - Re: [PATCH v5 02/10] perf record: implement -f,--mmap-flush=<threshold> option

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Date:   Thu, 7 Mar 2019 11:28:32 +0300
From:   Alexey Budankov <alexey.budankov@...ux.intel.com>
To:     Jiri Olsa <jolsa@...hat.com>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        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 v5 02/10] perf record: implement
 -f,--mmap-flush=<threshold> option


On 05.03.2019 15:25, Jiri Olsa wrote:
> On Fri, Mar 01, 2019 at 06:41:44PM +0300, Alexey Budankov wrote:
> 
> SNIP
> 
>>  static int process_synthesized_event(struct perf_tool *tool,
>>  				     union perf_event *event,
>>  				     struct perf_sample *sample __maybe_unused,
>> @@ -543,7 +566,8 @@ static int record__mmap_evlist(struct record *rec,
>>  	if (perf_evlist__mmap_ex(evlist, opts->mmap_pages,
>>  				 opts->auxtrace_mmap_pages,
>>  				 opts->auxtrace_snapshot_mode,
>> -				 opts->nr_cblocks, opts->affinity) < 0) {
>> +				 opts->nr_cblocks, opts->affinity,
>> +				 opts->mmap_flush) < 0) {
>>  		if (errno == EPERM) {
>>  			pr_err("Permission error mapping pages.\n"
>>  			       "Consider increasing "
>> @@ -733,7 +757,7 @@ static void record__adjust_affinity(struct record *rec, struct perf_mmap *map)
>>  }
>>  
>>  static int record__mmap_read_evlist(struct record *rec, struct perf_evlist *evlist,
>> -				    bool overwrite)
>> +				    bool overwrite, bool sync)
>>  {
>>  	u64 bytes_written = rec->bytes_written;
>>  	int i;
>> @@ -756,12 +780,19 @@ static int record__mmap_read_evlist(struct record *rec, struct perf_evlist *evli
>>  		off = record__aio_get_pos(trace_fd);
>>  
>>  	for (i = 0; i < evlist->nr_mmaps; i++) {
>> +		u64 flush = MMAP_FLUSH_DEFAULT;
> 
> hum, why does this need the initial value?

Compiler reported some warning or even error so staying on the safe side.

> 
>>  		struct perf_mmap *map = &maps[i];
>>  
>>  		if (map->base) {
>>  			record__adjust_affinity(rec, map);
>> +			if (sync) {
>> +				flush = map->flush;
>> +				map->flush = MMAP_FLUSH_DEFAULT;
>> +			}
>>  			if (!record__aio_enabled(rec)) {
>>  				if (perf_mmap__push(map, rec, record__pushfn) != 0) {
>> +					if (sync)
>> +						map->flush = flush;
>>  					rc = -1;
>>  					goto out;
>>  				}
>> @@ -774,10 +805,14 @@ static int record__mmap_read_evlist(struct record *rec, struct perf_evlist *evli
>>  				idx = record__aio_sync(map, false);
>>  				if (perf_mmap__aio_push(map, rec, idx, record__aio_pushfn, &off) != 0) {
>>  					record__aio_set_pos(trace_fd, off);
>> +					if (sync)
>> +						map->flush = flush;
>>  					rc = -1;
>>  					goto out;
>>  				}
>>  			}
>> +			if (sync)
>> +				map->flush = flush;
> 
> is there a point to set this back in case of sync == true?
> we are going out at this point, right?

Right, but function should work independently of any external assumption. 

~Alexey

> 
> jirka
>