Re: [PATCH v5 07/10] perf record: implement -z,--compression_level=n option and compression

Jiri Olsa
2019-03-08T10:47:04Z

On Thu, Mar 07, 2019 at 06:26:47PM +0300, Alexey Budankov wrote:
>
> On 07.03.2019 15:14, Jiri Olsa wrote:
> > On Thu, Mar 07, 2019 at 11:39:46AM +0300, Alexey Budankov wrote:
> >>
> >> On 05.03.2019 15:25, Jiri Olsa wrote:
> >>> On Fri, Mar 01, 2019 at 06:58:32PM +0300, Alexey Budankov wrote:
> >>>
> >>> SNIP
> >>>
> >>>>
> >>>> /*
> >>>> * Increment md->refcount to guard md->data[idx] buffer
> >>>> @@ -350,7 +357,7 @@ int perf_mmap__aio_push(struct perf_mmap *md, void *to, int idx,
> >>>> md->prev = head;
> >>>> perf_mmap__consume(md);
> >>>>
> >>>> - rc = push(to, &md->aio.cblocks[idx], md->aio.data[idx], size0 + size, *off);
> >>>> + rc = push(to, md->aio.data[idx], size0 + size, *off, &md->aio.cblocks[idx]);
> >>>> if (!rc) {
> >>>> *off += size0 + size;
> >>>> } else {
> >>>> @@ -556,13 +563,15 @@ int perf_mmap__read_init(struct perf_mmap *map)
> >>>> }
> >>>>
> >>>> int perf_mmap__push(struct perf_mmap *md, void *to,
> >>>> - int push(struct perf_mmap *map, void *to, void *buf, size_t size))
> >>>> + int push(struct perf_mmap *map, void *to, void *buf, size_t size),
> >>>> + perf_mmap__compress_fn_t compress, void *comp_data)
> >>>> {
> >>>> u64 head = perf_mmap__read_head(md);
> >>>> unsigned char *data = md->base + page_size;
> >>>> unsigned long size;
> >>>> void *buf;
> >>>> int rc = 0;
> >>>> + size_t mmap_len = perf_mmap__mmap_len(md);
> >>>>
> >>>> rc = perf_mmap__read_init(md);
> >>>> if (rc < 0)
> >>>> @@ -574,7 +583,10 @@ int perf_mmap__push(struct perf_mmap *md, void *to,
> >>>> buf = &data[md->start & md->mask];
> >>>> size = md->mask + 1 - (md->start & md->mask);
> >>>> md->start += size;
> >>>> -
> >>>> + if (compress) {
> >>>> + size = compress(comp_data, md->data, mmap_len, buf, size);
> >>>> + buf = md->data;
> >>>> + }
> >>>> if (push(md, to, buf, size) < 0) {
> >>>> rc = -1;
> >>>> goto out;
> >>>
> >>> when we discussed the compress callback should be another layer
> >>> in perf_mmap__push I was thinking more of the layered/fifo design,
> >>> like:
> >>>
> >>> normaly we call:
> >>>
> >>> perf_mmap__push(... push = record__pushfn ...)
> >>> -> reads mmap data and calls push(data), which translates as:
> >>>
> >>> record__pushfn(data);
> >>> - which stores the data
> >>>
> >>>
> >>> for compressed it'd be:
> >>>
> >>> perf_mmap__push(... push = compressed_push ...)
> >>>
> >>> -> reads mmap data and calls push(data), which translates as:
> >>>
> >>> compressed_push(data)
> >>> -> reads data, compresses them and calls, next push callback in line:
> >>>
> >>> record__pushfn(data)
> >>> - which stores the data
> >>>
> >>>
> >>> there'd need to be the logic for compressed_push to
> >>> remember the 'next push' function
> >>
> >> That is suboptimal for AIO. Also compression is an independent operation that
> >> could be applied on any of push stages you mean.
> >
> > not sure what you mean by suboptimal, but I think
> > that it can still happen in subsequent push callback
> >
> >>
> >>>
> >>> but I think this was the original idea behind the
> >>> perf_mmap__push -> it gets the data and pushes them for
> >>> the next processing.. it should stay as simple as that
> >>
> >> Agree on keeping simplicity and, at the moment, there is no any push to the next
> >> processing in the code so provided implementation fits as for serial as for AIO
> >> at the same time sticking to simplicity as much as possibly. If you see something
> >> that would fit better please speak up and share.
> >
> > I have to insist that perf_mmap__push stays untouched
> > and we do other processing in the push callbacks
>
> What is about perf_mmap__aio_push()?
>
> Without compression it does
> memcpy(), memcpy(), aio_push()
>
> With compression its does
> memcpy_with_compression(), memcpy_with_compression(), aio_push()

so to be on the same page.. normal processing without compression is:

perf_mmap__push does:
push(mmap buf)
record__pushfn
record__write
write(buf)

perf_mmap__aio_push does:
memcpy(aio buf, mmap buf)
push(aio buf)
record__aio_pushfn
record__aio_write
aio_write(aio buf)

and for compression it would be:

perf_mmap__push does:
push(mmap buf)
compress_push
memcpy(compress buffer, mmapbuf) EXTRA copy
record__pushfn
record__write
write(buf)

perf_mmap__aio_push does:
memcpy(aio buf, mmap buf)
memcpy(compress buffer, mmapbuf) EXTRA copy
push(aio buf)
record__aio_pushfn
record__aio_write
aio_write(aio buf)

side note: that actualy makes me think why do we even have perf_mmap__aio_push,
it looks like we could copy the buf in the callback push function with no harm?

so.. there's one extra memcpy for compression, is it right?
I might miss some part which makes this scheme unusable..

thanks,
jirka