Commit Graph

12 Commits

Author SHA1 Message Date
Denis Vlasenko 4277eedd79 vsprintf.c: optimizing, part 2: base 10 conversion speedup, v2
Optimize integer-to-string conversion in vsprintf.c for base 10.  This is
by far the most used conversion, and in some use cases it impacts
performance.  For example, top reads /proc/$PID/stat for every process, and
with 4000 processes decimal conversion alone takes noticeable time.

Using code from

http://www.cs.uiowa.edu/~jones/bcd/decimal.html
(with permission from the author, Douglas W. Jones)

binary-to-decimal-string conversion is done in groups of five digits at
once, using only additions/subtractions/shifts (with -O2; -Os throws in
some multiply instructions).

On i386 arch gcc 4.1.2 -O2 generates ~500 bytes of code.

This patch is run tested. Userspace benchmark/test is also attached.
I tested it on PIII and AMD64 and new code is generally ~2.5 times
faster. On AMD64:

# ./vsprintf_verify-O2
Original decimal conv: .......... 151 ns per iteration
Patched decimal conv:  .......... 62 ns per iteration
Testing correctness
12895992590592 ok...        [Ctrl-C]
# ./vsprintf_verify-O2
Original decimal conv: .......... 151 ns per iteration
Patched decimal conv:  .......... 62 ns per iteration
Testing correctness
26025406464 ok...        [Ctrl-C]

More realistic test: top from busybox project was modified to
report how many us it took to scan /proc (this does not account
any processing done after that, like sorting process list),
and then I test it with 4000 processes:

#!/bin/sh
i=4000
while test $i != 0; do
    sleep 30 &
    let i--
done
busybox top -b -n3 >/dev/null

on unpatched kernel:

top: 4120 processes took 102864 microseconds to scan
top: 4120 processes took 91757 microseconds to scan
top: 4120 processes took 92517 microseconds to scan
top: 4120 processes took 92581 microseconds to scan

on patched kernel:

top: 4120 processes took 75460 microseconds to scan
top: 4120 processes took 66451 microseconds to scan
top: 4120 processes took 67267 microseconds to scan
top: 4120 processes took 67618 microseconds to scan

The speedup comes from much faster generation of /proc/PID/stat
by sprintf() calls inside the kernel.

Signed-off-by: Douglas W Jones <jones@cs.uiowa.edu>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-07-16 09:05:52 -07:00
Denis Vlasenko b39a734097 vsprintf.c: optimizing, part 1 (easy and obvious stuff)
* There is no point in having full "0...9a...z" constant vector,
  if we use only "0...9a...f" (and "x" for "0x").

* Post-decrement usually needs a few more instructions, so use
  pre decrement instead where makes sense:
-       while (i < precision--) {
+       while (i <= --precision) {

* if base != 10 (=> base 8 or 16), we can avoid using division
  in a loop and use mask/shift, obtaining much faster conversion.
  (More complex optimization for base 10 case is in the second patch).

Overall, size vsprintf.o shows ~80 bytes smaller text section
with this patch applied.

Signed-off-by: Douglas W Jones <jones@cs.uiowa.edu>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-07-16 09:05:52 -07:00
Johannes Berg c6b40d16d1 fix sscanf %n match at end of input string
I was playing with some code that sometimes got a string where a %n
match should have been done where the input string ended, for example
like this:

  sscanf("abc123", "abc%d%n", &a, &n);  /* doesn't work */
  sscanf("abc123a", "abc%d%n", &a, &n); /* works */

However, the scanf function in the kernel doesn't convert the %n in that
case because it has already matched the complete input after %d and just
completely stops matching then. This patch fixes that.

[akpm@linux-foundation.org: cleanups]
Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-05-08 11:15:05 -07:00
Jeremy Fitzhardinge 11443ec7d9 Add kvasprintf()
Add a kvasprintf() function to complement kasprintf().

No in-tree users yet, but I have some coming up.

[akpm@linux-foundation.org: EXPORT it]
Signed-off-by: Jeremy Fitzhardinge <jeremy@xensource.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Keir Fraser <keir@xensource.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-04-30 16:40:40 -07:00
Martin Peschke ea6f3281a1 [PATCH] scnprintf(): fix a comment
The return value of scnprintf() never exceeds @size.

Signed-off-by: Martin Peschke <mp3@de.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-02-12 09:48:28 -08:00
Robert P. J. Day 72fd4a35a8 [PATCH] Numerous fixes to kernel-doc info in source files.
A variety of (mostly) innocuous fixes to the embedded kernel-doc content in
source files, including:

  * make multi-line initial descriptions single line
  * denote some function names, constants and structs as such
  * change erroneous opening '/*' to '/**' in a few places
  * reword some text for clarity

Signed-off-by: Robert P. J. Day <rpjday@mindspring.com>
Cc: "Randy.Dunlap" <rdunlap@xenotime.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-02-11 10:51:32 -08:00
Linus Torvalds 0a6047eef1 Fix vsnprintf off-by-one bug
The recent vsnprintf() fix introduced an off-by-one, and it's now
possible to overrun the target buffer by one byte.

The "end" pointer points to past the end of the buffer, so if we
have to truncate the result, it needs to be done though "end[-1]".

[ This is just an alternate and simpler patch to one proposed by Andrew
  and Jeremy, who actually noticed the problem ]

Acked-by: Andrew Morton <akpm@osdl.org>
Acked-by: Jeremy Fitzhardinge <jeremy@goop.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-06-28 17:09:34 -07:00
Jeremy Fitzhardinge e905914f96 [PATCH] Implement kasprintf
Implement kasprintf, a kernel version of asprintf.  This allocates the
memory required for the formatted string, including the trailing '\0'.
Returns NULL on allocation failure.

Signed-off-by: Jeremy Fitzhardinge <jeremy@xensource.com>
Signed-off-by: Chris Wright <chrisw@sous-sol.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-06-25 10:01:23 -07:00
Jeremy Fitzhardinge f796937a06 [PATCH] Fix bounds check in vsnprintf, to allow for a 0 size and NULL buffer
This change allows callers to use a 0-byte buffer and a NULL buffer pointer
with vsnprintf, so it can be used to determine how large the resulting
formatted string will be.

Previously the code effectively treated a size of 0 as a size of 4G (on
32-bit systems), with other checks preventing it from actually trying to
emit the string - but the terminal \0 would still be written, which would
crash if the buffer is NULL.

This change changes the boundary check so that 'end' points to the putative
location of the terminal '\0', which is only written if size > 0.

vsnprintf still allows the buffer size to be set very large, to allow
unbounded buffer sizes (to implement sprintf, etc).

[akpm@osdl.org: fix long-vs-longlong confusion]
Signed-off-by: Jeremy Fitzhardinge <jeremy@xensource.com>
Signed-off-by: Chris Wright <chrisw@sous-sol.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-06-25 10:01:23 -07:00
Tim Schmielau 4e57b68178 [PATCH] fix missing includes
I recently picked up my older work to remove unnecessary #includes of
sched.h, starting from a patch by Dave Jones to not include sched.h
from module.h. This reduces the number of indirect includes of sched.h
by ~300. Another ~400 pointless direct includes can be removed after
this disentangling (patch to follow later).
However, quite a few indirect includes need to be fixed up for this.

In order to feed the patches through -mm with as little disturbance as
possible, I've split out the fixes I accumulated up to now (complete for
i386 and x86_64, more archs to follow later) and post them before the real
patch.  This way this large part of the patch is kept simple with only
adding #includes, and all hunks are independent of each other.  So if any
hunk rejects or gets in the way of other patches, just drop it.  My scripts
will pick it up again in the next round.

Signed-off-by: Tim Schmielau <tim@physik3.uni-rostock.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2005-10-30 17:37:32 -08:00
Al Viro 8032230694 [PATCH] %t... in vsnprintf
handling of %t... (ptrdiff_t) in vsnprintf

Signed-off-by: Al Viro <viro@parcelfarce.linux.theplanet.co.uk>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2005-08-23 18:43:46 -07:00
Linus Torvalds 1da177e4c3 Linux-2.6.12-rc2
Initial git repository build. I'm not bothering with the full history,
even though we have it. We can create a separate "historical" git
archive of that later if we want to, and in the meantime it's about
3.2GB when imported into git - space that would just make the early
git days unnecessarily complicated, when we don't have a lot of good
infrastructure for it.

Let it rip!
2005-04-16 15:20:36 -07:00