linux-kernel - Re: [PATCH v11 2/3]: perf record: enable asynchronous trace writing

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Date:   Mon, 8 Oct 2018 12:57:20 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     Alexey Budankov <alexey.budankov@...ux.intel.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Andi Kleen <ak@...ux.intel.com>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v11 2/3]: perf record: enable asynchronous trace writing

On Mon, Oct 08, 2018 at 09:17:11AM +0300, Alexey Budankov wrote:

SNIP

>  static int record__mmap_read_evlist(struct record *rec, struct perf_evlist *evlist,
>  				    bool overwrite)
>  {
> @@ -520,7 +644,10 @@ static int record__mmap_read_evlist(struct record *rec, struct perf_evlist *evli
>  	int i;
>  	int rc = 0;
>  	struct perf_mmap *maps;
> -
> +#ifdef HAVE_AIO_SUPPORT
> +	int trace_fd = rec->data.file.fd;
> +	off_t off;
> +#endif
>  	if (!evlist)
>  		return 0;
>  
> @@ -531,14 +658,34 @@ static int record__mmap_read_evlist(struct record *rec, struct perf_evlist *evli
>  	if (overwrite && evlist->bkw_mmap_state != BKW_MMAP_DATA_PENDING)
>  		return 0;
>  
> +#ifdef HAVE_AIO_SUPPORT
> +	off = lseek(trace_fd, 0, SEEK_CUR);
> +#endif
>  	for (i = 0; i < evlist->nr_mmaps; i++) {
>  		struct perf_mmap *map = &maps[i];
>  
>  		if (map->base) {
> -			if (perf_mmap__push(map, rec, record__pushfn) != 0) {
> -				rc = -1;
> -				goto out;
> +#ifdef HAVE_AIO_SUPPORT
> +			if (!rec->opts.nr_cblocks) {
> +#endif
> +				if (perf_mmap__push(map, rec, record__pushfn) != 0) {
> +					rc = -1;
> +					goto out;
> +				}
> +#ifdef HAVE_AIO_SUPPORT
> +			} else {
> +				/*
> +				 * Call record__aio_sync() to wait till map->data buffer
> +				 * becomes available after previous aio write request.
> +				 */
> +				record__aio_sync(map);
> +				if (perf_mmap__aio_push(map, rec, record__aio_pushfn, &off) != 0) {
> +					lseek(trace_fd, off, SEEK_SET);
> +					rc = -1;
> +					goto out;
> +				}
>  			}
> +#endif

I really don't like this.. let's have some aio_... function with its
dummy counterpart to be called in here.. and again.. if we realyl must
have this compiled optionaly, which I'm not convinced of

jirka