I'm no hardware nut, but.. [LWN.net]

I'm no hardware nut, but..

Posted Oct 2, 2008 17:01 UTC (Thu) by Oddscurity (guest, #46851)
In reply to: I'm no hardware nut, but.. by xav
Parent article: Low-level tracing plumbing

Not only that, but it'll possibly be just the packing. Unpacking and collating data can be done in userspace, and possibly offline after enough trace data's been collected.

Having dense fields like this also means a lot more of these will fit in cache.

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I'm no hardware nut, but..

Posted Oct 2, 2008 21:51 UTC (Thu) by fuhchee (guest, #40059) [Link] (2 responses)

> Not only that, but it'll possibly be just the packing. Unpacking and
> collating data can be done in userspace, and possibly offline after enough
> trace data's been collected.

OTOH, Linus wanted to people to be able to use this tracing stuff with
just a cat/grep, which seems to eschew *requiring* special userspace tools
for unpacking.

I'm no hardware nut, but..

Posted Oct 3, 2008 23:31 UTC (Fri) by tbird20d (subscriber, #1901) [Link] (1 responses)

It could still be kernel code doing the unpacking, just not at trace-time. This preserves the ability to use cat & grep, while still omitting the unpacking overhead during trace itself.

I'm no hardware nut, but..

Posted Oct 3, 2008 23:43 UTC (Fri) by fuhchee (guest, #40059) [Link]

> It could still be kernel code doing the unpacking, just not at trace-time.

If the kernel isn't going to host huge history buffers, then
conversions will in general have to be done essentially online,
probably deferred only a bit.