Re: [PATCH 5/7 v6] trace, RAS: Add eMCA trace event interface

From: Chen, Gong
Date: Tue Jun 03 2014 - 05:04:14 EST

On Mon, Jun 02, 2014 at 12:57:48PM -0400, Steven Rostedt wrote:
> Also matters how big you expect these events to be. If you get a
> "christmas tree" set of flags, how big will that event grow with all
> the descriptions attached?
> The max event size after all headers is 4056 bytes. If you go over
> that, the event is ignored.
Hi, Steven

Normally, the length of one eMCA trace record is between 200 and 256 bytes.
Once CMCI storm happens, before it is turned into poll mode, there are
about ~15 CMCI events are recorded, because I don't use rate limit for
trace so they should be recorded so seriously, some records will be lost.
But they are repeated and similar records so maybe the *lost* is not a
big issue.

Return to how to print trace record. To avoid buffer waste, I need to
print data when TP_printk called, in the meanwhile, the print content
is an array of [name, value], but we don't know how many items are
valid. Here is the question: I can't create a dynamic printk format
like "%s %d, %s %d, ..." in TP_printk. So the only way to me is
printking them all, even some of them are invalid, which means an 12
group "%s %d", or somthing like "%.*s" to make output format graceful.
This is what we want?

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