[systemd-devel] [PATCH 2/2] compress: add benchmark-style test

[Kay Sievers]

On Mon, Jul 7, 2014 at 9:40 PM, Zbigniew Jędrzejewski-Szmek
<zbyszek at in.waw.pl> wrote:
> On Mon, Jul 07, 2014 at 09:35:06PM +0300, Uoti Urpala wrote:
>> On Sat, 2014-07-05 at 20:56 +0200, Zbigniew Jędrzejewski-Szmek wrote:
>> > This is useful to test the behaviour of the compressor for various buffer
>> > sizes.
>> >
>> > Time is limited to a minute per compression, since otherwise, when LZ4
>> > takes more than a second which is necessary to reduce the noise, XZ
>> > takes more than 10 minutes.
>> >
>> > % build/test-compress-benchmark (without time limit)
>> > XZ: compressed & decompressed 2535300963 bytes in 794.57s (3.04MiB/s), mean compresion 99.95%, skipped 3570 bytes
>> > LZ4: compressed & decompressed 2535303543 bytes in 1.56s (1550.07MiB/s), mean compresion 99.60%, skipped 990 bytes
>>
>> Like your earlier comparison, this compares the wrong thing. If
>> compression speed matters more than best compression ratio, you
>> shouldn't use the default settings for xz. If you want to compare with
>> LZ4, this benchmark should at least compare the equivalent of "xz -0".

> The comparison should be done for whatever setting is used in journald
> and/or coredump.

No, The current defaults are irrelevant.

The comparison should be done with values that indicate that
introducing a new compression algorithm is needed. If xz *can* be
instructed to reach acceptable results, we would better stick with it.

Kay