* David Ahern <[email protected]> wrote:
> +--out-pages=::
> + Number of pages to mmap while writing data to file (must be a power of
> two).
> + Specification can be appended with unit character - B/K/M/G. The
> + size is rounded up to have nearest pages power of two value.
So why doesn't the code automatically round down (or up) to the next power
of 2 limit? We use computers to solve problems, not to introduce
additional ones! ;-)
> +/* output file mmap'ed N chunks at a time */
> +#define MMAP_OUTPUT_SIZE (64*1024*1024)
I suspect the --out-pages help text should mention that the default is
64M?
> struct perf_record {
> struct perf_tool tool;
> struct perf_record_opts opts;
> +
> + /* for MMAP based file writes */
> + void *mmap_addr;
> + u64 mmap_offset; /* current location within
> mmap */
> + unsigned int mmap_out_pages; /* user configurable option */
> + size_t mmap_out_size; /* size of mmap segments */
> + bool use_mmap;
So I think it makes sense for such a group of fields to get its own
record.mmap sub-structure and be referenced via:
rec->mmap.addr
rec->mmap.offset
rec->mmap.out_pages
...
Such sub-structures make the semantic grouping easier to see, etc.
> +static int do_mmap_output(struct perf_record *rec, void *buf, size_t size)
> +{
> + struct perf_data_file *file = &rec->file;
> + u64 remaining;
> + off_t offset;
> +
> + if (rec->mmap_addr == NULL) {
> +do_mmap:
> + offset = rec->session->header.data_offset + rec->bytes_written;
> + if (offset < (ssize_t) rec->mmap_out_size) {
> + rec->mmap_offset = offset;
> + offset = 0;
> + } else
> + rec->mmap_offset = 0;
(Nit: unbalanced curly braces.)
> +
> + /* extend file to include a new mmap segment */
> + if (ftruncate(file->fd, offset + rec->mmap_out_size) != 0) {
> + pr_err("ftruncate failed\n");
> + return -1;
> + }
> +
> + rec->mmap_addr = mmap(NULL, rec->mmap_out_size,
> + PROT_WRITE | PROT_READ, MAP_SHARED,
> + file->fd, offset);
> +
> + if (rec->mmap_addr == MAP_FAILED) {
> + pr_err("mmap failed: %d: %s\n", errno, strerror(errno));
> + /* reset file size */
> + ftruncate(file->fd, offset);
> + return -1;
> + }
> + }
I think this branch should move into its well-named helper inline
function.
> +
> + remaining = rec->mmap_out_size - rec->mmap_offset;
> +
> + if (size > remaining) {
> + memcpy(rec->mmap_addr + rec->mmap_offset, buf, remaining);
> + rec->bytes_written += remaining;
> +
> + size -= remaining;
> + buf += remaining;
> +
> + munmap(rec->mmap_addr, rec->mmap_out_size);
> + goto do_mmap;
> + }
> +
> + if (size) {
> + memcpy(rec->mmap_addr + rec->mmap_offset, buf, size);
> + rec->bytes_written += size;
> + rec->mmap_offset += size;
> + }
One-one line of comment that explains what these two branches do would be
nice.
> static int write_output(struct perf_record *rec, void *buf, size_t size)
> {
> struct perf_data_file *file = &rec->file;
>
> + if (rec->use_mmap)
> + return do_mmap_output(rec, buf, size);
> +
> while (size) {
> int ret = write(file->fd, buf, size);
I think to make it symmetric, the !use_mmap case should be moved into a
helper inline function as well. That way write_output() is just a
meta-function calling handlers, not a mixture of real logic and
demultiplexing of operations ...
> @@ -429,6 +498,12 @@ static int __cmd_record(struct perf_record *rec, int
> argc, const char **argv)
> goto out_delete_session;
> }
>
> + if (!file->is_pipe && rec->mmap_out_size) {
> + if (rec->mmap_out_pages)
> + rec->mmap_out_size = rec->mmap_out_pages * page_size;
> + rec->use_mmap = true;
> + }
This should move into a separate inline as well, named mmap_init() or so.
> @@ -544,6 +619,24 @@ static int __cmd_record(struct perf_record *rec, int
> argc, const char **argv)
> }
> }
>
> + if (rec->use_mmap) {
> + off_t len = rec->session->header.data_offset +
> rec->bytes_written;
> + int fd = rec->file.fd;
> +
> + rec->use_mmap = false;
> + munmap(rec->mmap_addr, rec->mmap_out_size);
> + rec->mmap_addr = NULL;
> +
> + if (ftruncate(fd, len) != 0)
> + pr_err("ftruncate failed\n");
> +
> + /*
> + * Set output pointer to end of file
> + * eg., needed for buildid processing
> + */
> + lseek(fd, len, SEEK_SET);
> + }
This should move into an inline as well. We really hate large, mixed-role
functions! :-)
> + OPT_CALLBACK(0, "out-pages", &record.mmap_out_pages, "pages",
> + "number of pages to use for output chunks.",
> + perf_evlist__parse_mmap_pages),
Nit: the short explanation here doesn't mention it at all to the user that
these 'out pages' are used in mmap.
Shouldn't it say:
"number of pages mmap()ed for output chunks."
?
Also, what happens if a user sets it to zero?
Thanks,
Ingo
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