Messages in this thread | | | Date | Thu, 26 Feb 2009 19:45:50 +0100 | From | Ingo Molnar <> | Subject | Re: [PATCH 1/3] add binary printf |
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* Frederic Weisbecker <fweisbec@gmail.com> wrote:
> On Thu, Feb 26, 2009 at 06:52:25PM +0100, Ingo Molnar wrote: > > > > * Frederic Weisbecker <fweisbec@gmail.com> wrote: > > > > > On Thu, Feb 26, 2009 at 06:43:03PM +0100, Ingo Molnar wrote: > > > > > > > > * Frederic Weisbecker <fweisbec@gmail.com> wrote: > > > > > > > > > On Thu, Feb 26, 2009 at 02:02:43PM +0100, Ingo Molnar wrote: > > > > > > > > > > > > * Frederic Weisbecker <fweisbec@gmail.com> wrote: > > > > > > > > > > > > > From: Lai Jiangshan <laijs@cn.fujitsu.com> > > > > > > > > > > > > > > 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@gmail.com: ported to latest -tip] > > > > > > > > > > > > > > Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com> > > > > > > > Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com> > > > > > > > Cc: Steven Rostedt <rostedt@goodmis.org> > > > > > > > --- > > > > > > > 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) > > > > > > > > > > > > > > > Ok. > > > > > > > > > > > > > > > > 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 > > > > > vbin_printf()). > > > > > > > > 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. > > > > > > > > Ingo > > > > > > Right, ok I'm on it. > > > > hm, it would still be nice to get vbin_printf() into the same > > scheme too. > > > > And i think we can do it by unconditionally tracking field type > > and width in the generic helper - instead of passing this across > > the abstraction barrier like your proposal did. vsnprintf() and > > bstr_printf() wont make use of it - but vbin_printf() will. > > > > Am i missing anything? > > > > Ingo > > Hm, I have some trouble to visualize it globally. > > vsnprintf: takes char * for dest and va_list as src, write formatted in dest > bstr_printf: takes char * as dest and u32 * as src, read from src is specialized > vbin_printf: takes u32 * buf as dest and va_list as src, write to dest is specialized > > The only thing that can be generic between the three is the > format decoding. All in-out operations must be abstracted if > we want a common interface from the three.
the thing is, the format decoding (and subsequent rendering of characters) is the only _interesting_ thing that happens here. So that is the thing we want to duplicate the least.
But yeah, i can see the complexity explosion with the abstraction interface. Too bad. And we use both new APIs.
Ingo
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