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SubjectRe: [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 int record__mmap_read_evlist(struct record *rec, struct perf_evlist *evlist,
> bool overwrite)
> {
> u64 bytes_written = rec->bytes_written;
> - int i;
> - int rc = 0;
> + int i, rc = 0;
> struct perf_mmap *maps;
> + int trace_fd = rec->session->data->file.fd;
> + struct aiocb **mmap_aio = rec->evlist->mmap_aio;
> + int mmap_aio_size = 0;
> + off_t off;
>
> if (!evlist)
> return 0;
> @@ -546,14 +620,17 @@ 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;
>
> + off = lseek(trace_fd, 0, SEEK_CUR);
> +

with async write, do we need to query/set the offset like this
all the time?

could we just keep/update the offset value in the 'struct perf_data_file'
and skip both lseek calls?

jirka

SNIP

>
> + record__mmap_read_sync(trace_fd, mmap_aio, mmap_aio_size, rec);
> +
> + lseek(trace_fd, off, SEEK_SET);
> +

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