linux-kernel - Re: [PATCH v2 2/2]: perf record: enable asynchronous trace writing

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Date:   Mon, 27 Aug 2018 10:43:33 +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>,
        linux-perf-users@...r.kernel.org
Subject: Re: [PATCH v2 2/2]: perf record: enable asynchronous trace writing

On Thu, Aug 23, 2018 at 07:47:01PM +0300, Alexey Budankov wrote:

SNIP

>  
>  static volatile int done;
> @@ -528,13 +530,85 @@ static struct perf_event_header finished_round_event = {
>  	.type = PERF_RECORD_FINISHED_ROUND,
>  };
>  
> +static int record__mmap_read_sync(int trace_fd, struct aiocb **cblocks,
> +		int cblocks_size, struct record *rec)
> +{
> +	size_t rem;
> +	ssize_t size;
> +	off_t rem_off;
> +	int i, aio_ret, aio_errno, do_suspend;
> +	struct perf_mmap *md;
> +	struct timespec timeout0 = { 0, 0 };
> +	struct timespec timeoutS = { 0, 1000 * 1000  * 1 };
> +
> +	if (!cblocks_size)
> +		return 0;
> +
> +	do {
> +		do_suspend = 0;
> +		nanosleep(&timeoutS, NULL);
> +		if (aio_suspend((const struct aiocb**)cblocks, cblocks_size, &timeout0)) {
> +			if (errno == EAGAIN || errno == EINTR) {
> +				do_suspend = 1;
> +				continue;
> +			} else {
> +				pr_err("failed to sync perf data, error: %m\n");
> +				break;
> +			}
> +		}
> +		for (i = 0; i < cblocks_size; i++) {

it looks like we could set up the async write to receive the signal
with the user pointer (sigev_value.sival_ptr), which would allow us
to get the finished descriptor right away and we wouldn't need
to iterate all of them and checking on them

jirka
> +			if (cblocks[i] == NULL) {
> +				continue;
> +			}
> +			aio_errno = aio_error(cblocks[i]);
> +			if (aio_errno == EINPROGRESS) {
> +				do_suspend = 1;
> +				continue;
> +			}

SNIP