linux-kernel - Re: [PATCH v2 2/4] perf record: implement -z=<level> and --mmap-flush=<thres> options

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Message-ID: <20190212130811.GA775@krava>
Date:   Tue, 12 Feb 2019 14:08:11 +0100
From:   Jiri Olsa <jolsa@...hat.com>
To:     Alexey Budankov <alexey.budankov@...ux.intel.com>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Andi Kleen <ak@...ux.intel.com>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 2/4] perf record: implement -z=<level> and
 --mmap-flush=<thres> options

On Mon, Feb 11, 2019 at 11:22:38PM +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 +574,8 @@ 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 "
> @@ -734,7 +766,7 @@ 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;
> @@ -757,12 +789,19 @@ 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;
>  		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;
>  				}
> @@ -775,10 +814,14 @@ 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;
>  		}

what's 'flush' and 'sync' for? also the above handling seems confusing,
why would you set it temporarily for default value if you let it set
by user command line option?

SNIP

> -static void perf_mmap__aio_munmap(struct perf_mmap *map __maybe_unused)
> +static void perf_mmap__aio_munmap_blocks(struct perf_mmap *map __maybe_unused)
>  {
>  }
>  #endif
> @@ -444,6 +468,8 @@ int perf_mmap__mmap(struct perf_mmap *map, struct mmap_params *mp, int fd, int c
>  				&mp->auxtrace_mp, map->base, fd))
>  		return -1;
>  
> +	map->flush = mp->flush;
> +
>  	return perf_mmap__aio_mmap(map, mp);
>  }
>  
> @@ -492,7 +518,7 @@ static int __perf_mmap__read_init(struct perf_mmap *md)
>  	md->start = md->overwrite ? head : old;
>  	md->end = md->overwrite ? old : head;
>  
> -	if (md->start == md->end)
> +	if ((md->end - md->start) < md->flush)
>  		return -EAGAIN;

we need document and explain this change in changelog in separate patch

thanks,
jirka