Re: [PATCH 1/3] add binary printf
From: Ingo Molnar
Date: Thu Feb 26 2009 - 12:43:41 EST
* Frederic Weisbecker <fweisbec@xxxxxxxxx> wrote:
> On Thu, Feb 26, 2009 at 02:02:43PM +0100, Ingo Molnar wrote:
> > * Frederic Weisbecker <fweisbec@xxxxxxxxx> wrote:
> > > From: Lai Jiangshan <laijs@xxxxxxxxxxxxxx>
> > >
> > > Impact: Add APIs for binary trace printk infrastructure
> > >
> > > vbin_printf(): write args to binary buffer, string is copied
> > > when "%s" is occurred.
> > >
> > > bstr_printf(): read from binary buffer for args and format a string
> > >
> > > [fweisbec@xxxxxxxxx: ported to latest -tip]
> > >
> > > Signed-off-by: Lai Jiangshan <laijs@xxxxxxxxxxxxxx>
> > > Signed-off-by: Frederic Weisbecker <fweisbec@xxxxxxxxx>
> > > Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
> > > ---
> > > include/linux/string.h | 7 +
> > > lib/Kconfig | 3 +
> > > lib/vsprintf.c | 442 ++++++++++++++++++++++++++++++++++++++++++++++++
> > > 3 files changed, 452 insertions(+), 0 deletions(-)
> > OK, it's a nice idea and speedup for printf based tracing -
> > which is common and convenient. Would you mind to post the
> > performance measurements you've done using the new bstr_printf()
> > facility? (the nanoseconds latency figures you did in the timer
> > irq in a system under load and on a system that is idle)
> > The new printf code itself should be done cleaner i think and is
> > not acceptable in its current form.
> > These two new functions:
> > > +#ifdef CONFIG_BINARY_PRINTF
> > > +/*
> > > + * bprintf service:
> > > + * vbin_printf() - VA arguments to binary data
> > > + * bstr_printf() - Binary data to text string
> > > + */
> > Duplicate hundreds of lines of code into three large functions
> > (vsnprintf, vbin_printf, bstr_printf). These functions only have
> > a difference in the way the argument list is iterated and the
> > way the parsed result is stored:
> > vsnprintf: iterates va_list, stores into string
> > bstr_printf: iterates bin_buf, stores into string
> > vbin_printf: iterates va_list, stores into bin_buf
> > We should try _much_ harder at unifying these functions before
> > giving up and duplicating them...
> > An opaque in_buf/out_buf handle plus two helper function
> > pointers passed in would be an obvious implementation.
> > That way we'd have a single generic (inline) function that knows
> > about the printf format itself:
> > __generic_printf(void *in_buf,
> > void *out_buf,
> > void * (*read_in_buf)(void **),
> > void * (*store_out_buf)(void **));
> > And we'd have various variants for read_in_buf and
> > store_out_buf. The generic function iterates the following way:
> > in_val = read_in_buf(&in_buf);
> > ...
> > store_out_buf(&out_buf, in_val);
> > (where in_val is wide enough to store a single argument.) The
> > iterators modify the in_buf / out_buf pointers. Argument
> > skipping can be done by reading the in-buf and not using it. I
> > think we can do it with just two iterator methods.
> > Or something like that - you get the idea. It can all be inlined
> > so that we'd end up with essentially the same vsnprint()
> > instruction sequence we have today.
> > Ingo
> Ok, I just looked deeply inside vsnprintf, and I don't think
> such a generic interface would allow that. We need to know the
> size of the argument, it's precision, width and flags.... And
> we need to know if we want to skip the non format char.
> What do you think of the following:
> __ generic_printf(void *in,
> void *out,
> void *(*read_in)(void **buf, int size),
> void *(store_char)(char *dst, char *end, char val, int field_width, int flags),
> void *(*store_string)(char *dst, char *end, char *val, int field_width, int precision, int flags),
> void *(*store_pointer)(char type, char *dst, char *end, void *val,
> int field_width, int precision, int flags),
> void *(*store_number)(char *dst, char *size, int base,int field_width, int precision, int flags),
> bool skip_non_format
> Well, something like that...
> read_in can advance the pointer to the buffer itself (buf can
> be a va_args or u32 *) and it returns a value, void * is
> generic for the type.
> The storage functions are more specialized because of the
> interpretation of flags, precision... So we can easily pass
> the usual string(), pointer(), .... that are already present
> in vsnprintf.c or use custom ones. They return the advanced
> dst pointer.
> And at last, skip_non_format will decide if we want to
> consider non-format characters from fmt to be copied as common
> %c characters or if we want to ignore them (useful for
hm, that indeed looks very wide - storing into a binary buffer
does complicate the iterator interface significantly.
But at least vsnprintf() and bstr_printf() could be unified -
they both output into a string buffer, just have different
methods to iterate arguments.
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