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SubjectRe: [PATCH 0/5 v2] Binary ftrace_printk
On Thu, Mar 05, 2009 at 05:53:58AM +0100, Frederic Weisbecker wrote:
>
> This new iteration addresses Steven's reviews.
> Notably:
>
> - only build the ftrace_printk format section if CONFIG_TRACING is set
> - be scheduler tracing safe (don't use preempt_enable directly from
> ftrace_printk to avoid tracing recursion)
> - fix a loss of format string when a module is unloaded. Since we can loose
> it on the ring-buffer if it is in overwrite mode, we don't keep track
> of the format given by the modules to free them. We just copy their
> ftrace_printk string format forever. Note that it is safe against duplicate
> strings since we verify if the string is already present in our list before
> allocating a new one.
>
> ---


tip:master has seen some changes concerning the tracing bits since this patchset
submission, notably the movement of ftrace_printk to include/kernel.h

These patches probably won't anymore apply properly.
Do you want me to rebase them against latest tip/master?

Or perhaps you prefer to wait for a Acked-by from Linus or Andrew?

Frederic.


> An new optimization is making its way to ftrace. Its purpose is to
> make ftrace_printk() consuming less memory and become faster.
>
> Written by Lai Jiangshan, the approach is to delay the formatting
> job from tracing time to output time.
> Currently, a call to ftrace_printk will format the whole string and
> insert it into the ring buffer. Then you can read it on /debug/tracing/trace
> file.
>
> The new implementation stores the address of the format string and
> the binary parameters into the ring buffer, making the packet more compact
> and faster to insert.
> Later, when the user exports the traces, the format string is retrieved
> with the binary parameters and the formatting job is eventually done.
>
> Here is the result of a small comparative benchmark while putting the following
> ftrace_printk on the timer interrupt. ftrace_printk is the old implementation,
> ftrace_bprintk is a the new one:
>
> ftrace_printk("This is the timer interrupt: %llu", jiffies_64);
>
> After some time running on low load (no X, no really active processes):
>
> ftrace_printk: duration average: 2044 ns, avg of bytes stored per entry: 39
> ftrace_bprintk: duration average: 1426 ns, avg of bytes stored per entry: 16
>
> Higher load (started X and launched a cat running on a X console looping on
> traces printing):
>
> ftrace_printk: duration average: 8812 ns
> ftrace_bprintk: duration average: 2611 ns
>
> Which means the new implementation can be 70 % faster on higher load.
> And it consumes lesser memory on the ring buffer.
>
> The three first patches rebase against latest -tip the ftrace_bprintk work done
> by Lai few monthes ago.
>
> The two others integrate ftrace_bprintk as a replacement for the old
> ftrace_printk implementation and factorize the printf style format decoding
> which is now used by three functions.
>
> Frederic Weisbecker (2):
> tracing/core: drop the old ftrace_printk implementation in favour of
> ftrace_bprintk
> vsprintf: unify the format decoding layer for its 3 users
>
> Lai Jiangshan (3):
> add binary printf
> ftrace: infrastructure for supporting binary record
> ftrace: add ftrace_bprintk()
>
> include/asm-generic/vmlinux.lds.h | 3 +
> include/linux/ftrace.h | 44 ++-
> include/linux/module.h | 5 +
> include/linux/string.h | 7 +
> kernel/module.c | 6 +
> kernel/trace/Kconfig | 1 +
> kernel/trace/Makefile | 1 +
> kernel/trace/trace.c | 141 +++---
> kernel/trace/trace.h | 8 +-
> kernel/trace/trace_functions_graph.c | 6 +-
> kernel/trace/trace_mmiotrace.c | 9 +-
> kernel/trace/trace_output.c | 31 +-
> kernel/trace/trace_output.h | 2 +
> kernel/trace/trace_printk.c | 138 +++++
> lib/Kconfig | 3 +
> lib/vsprintf.c | 1006 ++++++++++++++++++++++++++--------
> 16 files changed, 1087 insertions(+), 324 deletions(-)
> create mode 100644 kernel/trace/trace_printk.c
>
>



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