linux-kernel - Re: [PATCH v5 07/10] perf record: implement -z,--compression

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Date:   Mon, 11 Mar 2019 11:56:00 +0100
From:   Jiri Olsa <jolsa@...hat.com>
To:     Alexey Budankov <alexey.budankov@...ux.intel.com>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Andi Kleen <ak@...ux.intel.com>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5 07/10] perf record: implement -z,--compression_level=n
 option and compression

On Sun, Mar 10, 2019 at 07:17:08PM +0300, Alexey Budankov wrote:

SNIP

> > 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?
> 
> Well, yes, perf_mmap__aio_push() can be avoided and perf_mmap__push() can be used
> as for serial as for AIO, moving all the specifics to record code from mmap.c,
> like this:
> 
> Serial
> 	perf_mmap__push(, record__pushfn)
>  	   push(), possibly two times
> 	      record__pushfn()
>                  if (-z) zstd_compress(map->base => map->data) <-- compressing memcpy()
>                  record__write(-z ? map->data, map->base)
> AIO
> 	record__aio_push()
> 	   perf_mmap__push(, record__aio_pushfn())
>               push(), possibly two times
>                  record__aio_pushfn()
>                     if (-z) zstd_compress(map->base => map->aio.data[i]) <--- compressing memcpy()
>                     else memcpy(map->base => map->aio.data[i]) <--- plain memcpy()
>            record__aio_write(map->aio.data[i]) 
> 
> So now it looks optimal as from performance and data loss reduction 
> perspective as from design perspective. What do you think?

yes, that looks much better.. so we'd have record__pushfn
for standard (serial) and record__aio_pushfn for AIO

thanks,
jirka