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

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Date:   Tue, 5 Mar 2019 13:25:34 +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 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

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

jirka