* [PATCH] fs: seq_file: optimize seq_pad()
@ 2014-09-10 9:20 Dmitry Voytik
2014-09-10 13:21 ` Al Viro
0 siblings, 1 reply; 3+ messages in thread
From: Dmitry Voytik @ 2014-09-10 9:20 UTC (permalink / raw)
To: Alexander Viro; +Cc: Tetsuo Handa, linux-kernel, linux-fsdevel, Dmitry Voytik
Use seq_putc() instead of seq_printf() in seq_pad() because the
former is faster.
Signed-off-by: Dmitry Voytik <voytikd@gmail.com>
---
fs/seq_file.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/fs/seq_file.c b/fs/seq_file.c
index 3857b72..fef338e 100644
--- a/fs/seq_file.c
+++ b/fs/seq_file.c
@@ -787,8 +787,10 @@ EXPORT_SYMBOL(seq_write);
void seq_pad(struct seq_file *m, char c)
{
int size = m->pad_until - m->count;
- if (size > 0)
- seq_printf(m, "%*s", size, "");
+
+ while (size-- > 0)
+ if (unlikely(seq_putc(m, ' ')))
+ return;
if (c)
seq_putc(m, c);
}
--
1.9.1
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH] fs: seq_file: optimize seq_pad()
2014-09-10 9:20 [PATCH] fs: seq_file: optimize seq_pad() Dmitry Voytik
@ 2014-09-10 13:21 ` Al Viro
2014-09-10 14:20 ` Dmitry Voytik
0 siblings, 1 reply; 3+ messages in thread
From: Al Viro @ 2014-09-10 13:21 UTC (permalink / raw)
To: Dmitry Voytik; +Cc: Tetsuo Handa, linux-kernel, linux-fsdevel
On Wed, Sep 10, 2014 at 01:20:19PM +0400, Dmitry Voytik wrote:
> Use seq_putc() instead of seq_printf() in seq_pad() because the
> former is faster.
_Solitary_ seq_putc() is certainly going to be faster, but that loop...
Do you have profiling results, or is it just an apriori "printf must
be sloooowwww"?
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] fs: seq_file: optimize seq_pad()
2014-09-10 13:21 ` Al Viro
@ 2014-09-10 14:20 ` Dmitry Voytik
0 siblings, 0 replies; 3+ messages in thread
From: Dmitry Voytik @ 2014-09-10 14:20 UTC (permalink / raw)
To: Al Viro; +Cc: Tetsuo Handa, linux-kernel, linux-fsdevel
On Wed, Sep 10, 2014 at 5:21 PM, Al Viro <viro@zeniv.linux.org.uk> wrote:
> On Wed, Sep 10, 2014 at 01:20:19PM +0400, Dmitry Voytik wrote:
>> Use seq_putc() instead of seq_printf() in seq_pad() because the
>> former is faster.
>
> _Solitary_ seq_putc() is certainly going to be faster, but that loop...
> Do you have profiling results, or is it just an apriori "printf must
> be sloooowwww"?
My fail, sorry. The commit message is little bit wrong. I meant that simple
looping of seq_putc() is faster than seq_printf(). I haven't done profilings.
I just realized that seq_printf() is more complex than simple loop
with seq_putc()
(no need to decode format string as in vsnprintf(), etc).
If I resend the patch with the following commit message:
Use a simple loop with seq_putc() instead of seq_printf() in seq_pad() as
this approach is faster due to less complexity in terms of machine cycles.
Would be it Okay?
Thank you for reviewing.
--
Best Regards,
Dmitry Voytik.
voytikd@gmail.com
^ permalink raw reply [flat|nested] 3+ messages in thread
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2014-09-10 9:20 [PATCH] fs: seq_file: optimize seq_pad() Dmitry Voytik
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