Messages in this thread |  | | | Date | Tue, 24 Feb 2009 12:17:18 -0500 | | From | Jason Baron <> | | Subject | Re: [PATCH 0/3] tracing/ftrace: ftrace_bprintk |
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On Tue, Feb 24, 2009 at 06:16:18AM +0100, Frederic Weisbecker wrote: > Hi, > > These three patches are part of a patchset posted by Lai Jiangshan in december 2008. > They introduce a binary version of ftrace_printk() called ftrace_bprintk() > > While having the same goal: print a generic message entry into the ring buffer, > their approaches are very different. > > - ftrace_printk() does the formatting job on tracing time, insert the whole resulting string > into the ring buffer, and then the string is printed on output time without a lot of modifications. > > - ftrace_bprintk() does no formatting on tracing time. Instead, it looks at the format string > to find the types and the numbers of the arguments and directly stores them as-is into the > ring-buffer. Then the format string is stored into the ring-buffer too, but only by its address, > it is not copied. Then on output time only, the final string is formatted and sent to the user. > This gives a result about as fast as a traditional tracer with fixed fields types, except that > we can print random types and numbers of fields here. > > > The first patch adds the generic support for binary formatting. > The second adds the support for binary print types on ftrace > and the last introduces ftrace_bprintk() which supports safely the modules > by listening on the module loading/unloading notifier to keep track of > unwanted freed format strings. > > Lai Jiangshan (3): > add binary printf > ftrace: infrastructure for supporting binary record > ftrace: add ftrace_bprintk() >
hi,
this seems like a really valuable feature....I'm just wondering about a couple of things.... If the 'brpintk tracer' in trace/trace_bprintk.c is just being used to set an enabled flag for printing out these binary records, then are we better off with just an option flag in the 'trace_options' file?
Second, can we somehow combine ftrace_printk() and ftrace_bprintk(), so that a developer can just use one interface? Perhaps, ftrace_printk calls ftrace_bprintk if binary option flag is set, otherwise, it just outputs things normally.
thanks,
-Jason
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