Re: [RFC PATCH] seq_file: Use seq_puts when seq_printf has only aformat with no args
From: Joe Perches
Date: Mon Mar 18 2013 - 22:41:47 EST
On Mon, 2013-03-18 at 13:59 -0700, Andrew Morton wrote:
> On Sat, 16 Mar 2013 17:54:47 +0000 Al Viro <viro@xxxxxxxxxxxxxxxxxx> wrote:
> > On Sat, Mar 16, 2013 at 06:50:44AM -0700, Joe Perches wrote:
> > > Instead of converting the 800 or so uses of seq_printf with
> > > a constant format (without a % substitution) to seq_puts,
> > > maybe there's another way to slightly speed up these outputs.
> > >
> > > Taking a similar approach to commit abd84d60eb
> > > ("tracing: Optimize trace_printk() with one arg to use trace_puts()")
> > > use the preprocessor to convert seq_printf(seq, "string constant")
> > > to seq_puts(seq, "string constant")
> > >
> > > By stringifying __VA_ARGS__, we can, at compile time, determine
> > > the number of args that are being passed to seq_printf() and
> > > call seq_puts or seq_printf appropriately.
> > >
> > > The actual function definition for seq_printf must now
> > > be enclosed in parenthesis to avoid further macro expansion.
> > Joe, would you mind showing me a single real-world case where that
> > "optimization" would really matter?
> There's also a small reduction in code footprint. We merge less
> significant things all day ;)
It's small. ~1kb x86/32 defconfig
$ size def/vmlinux.o*
text data bss dec hex filename
9296433 661732 1822196 11780361 b3c109 def/vmlinux.o.new
9297361 661732 1822196 11781289 b3c4a9 def/vmlinux.o.old
> > NAKed-because: GAFL
I'm delighted to have a ViroGAFL score of 2.
> Yeah, that macro thing should be nuked from orbit.
It is kinda cute though.
Perhaps it could become something more generic like:
#define __VA_ARGS__EXIST(...) \
int ret; \
char __va_args__exist = __stringify(__VA_ARGS__); \
ret = sizeof(__va_args__exist) != 1; \
so the hacky ugliness is confined.
> Please let's add the
> checkpatch rule (resend when convenient with clean changelog, please)
> and if people want to send "convert seq_printk to seq_puts" patches to
> Jan and he takes them into the trivial tree then all is good.
I'll resend it.
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/