Re: idea: MAC level compression & crypto

Benno Senoner (sbenno@gardena.net)
Sun, 29 Aug 1999 02:27:23 +0200


On Sun, 29 Aug 1999, Helge Hafting wrote:
> > - The disk performance decreases by 10-25% when I increase the CPU load in
> > the "latencytest" bench.
> The server people certainly won't like that.

Nor I do.
But I'm still not convinced it this is really possible.
You have to check rescheduling during
kernel memcopy routines , or large mem blocks moves, since at 100MB/sec
1MB of data = 10msec latency.
It not an easy task to keep latencies down.
Maybe the checking generates some cache misses and decreases performance,
especially when copying many small blocks ?

>
> > I think most of us want to have these "low-latency" features in the upcoming
> > 2.4 kernel since it will make Linux a very good _MULTIMEDIA_OS_.
>
> Everybody wants low-latency. But Linus looked at the patches and said
> "If *that* helps then something is wrong. Those functions shouldn't
> take so much time!"
> He then refused to accept patches that "paper over" a bug. Instead he
> wanted the bug fixed (i.e. make the functions in question take less
> time - they way they should.)

Agreed, but the question is: is some kernel hacker motivated to do
implement this before 2.4 ?

> That would give the same low latency without hurting disk performance under
> load.

I'm not 100%sure about this ..
Nothing comes at zero cost..

regards,
Benno.

--
Benno Senoner
E-Mail: sbenno@gardena.net
Linux scheduling latency benchmarks
http://www.gardena.net/benno/linux/audio

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