* [PATCH 1/1] lib: small update for strlen, strnlen, use less cpu instructions
@ 2015-06-16 18:51 Orestes Leal Rodriguez
0 siblings, 0 replies; 6+ messages in thread
From: Orestes Leal Rodriguez @ 2015-06-16 18:51 UTC (permalink / raw)
To: linux-kernel
Very small update to strlen and strnlen that now use less cpu
instructions by using a counter to avoid the memory addresses
substraction to find the length of the string.
Signed-off-by: Orestes Leal Rodriguez <lukes357@gmail.com>
---
diff --git a/lib/string.c b/lib/string.c
index 992bf30..c873436 100644
--- a/lib/string.c
+++ b/lib/string.c
@@ -17,6 +17,10 @@
* * Sat Feb 09 2002, Jason Thomas <jason@topic.com.au>,
* Matthew Hawkins <matt@mh.dropbear.id.au>
* - Kissed strtok() goodbye
+ *
+ * * Tuesday June 16 2015, Orestes Leal Rodriguez <lukes357@gmail.com>
+ * - strlen, strnlen: by using a single counter we use less cpu
instructions
+ * by avoiding substracting the memory addresses before return
*/
#include <linux/types.h>
@@ -401,11 +405,11 @@ EXPORT_SYMBOL(strim);
*/
size_t strlen(const char *s)
{
- const char *sc;
+ size_t sz = 0;
- for (sc = s; *sc != '\0'; ++sc)
- /* nothing */;
- return sc - s;
+ for (; *s++ != '\0'; sz++)
+ /* empty */;
+ return sz;
}
EXPORT_SYMBOL(strlen);
#endif
@@ -418,12 +422,13 @@ EXPORT_SYMBOL(strlen);
*/
size_t strnlen(const char *s, size_t count)
{
- const char *sc;
+ size_t sz = 0;
- for (sc = s; count-- && *sc != '\0'; ++sc)
- /* nothing */;
- return sc - s;
+ for (; count-- && *s++ != '\0'; sz++)
+ /* empty */;
+ return sz;
}
+
EXPORT_SYMBOL(strnlen);
#endif
^ permalink raw reply related [flat|nested] 6+ messages in thread
* Re: [PATCH 1/1] lib: small update for strlen, strnlen, use less cpu instructions
2015-06-17 20:07 ` Richard Weinberger
@ 2015-06-19 3:11 ` Orestes Leal Rodriguez
0 siblings, 0 replies; 6+ messages in thread
From: Orestes Leal Rodriguez @ 2015-06-19 3:11 UTC (permalink / raw)
To: Richard Weinberger; +Cc: bp, linux-kernel
thank you for your comments, begginer mistakes (I guess),
On 6/17/15, Richard Weinberger <richard@nod.at> wrote:
> Am 17.06.2015 um 00:51 schrieb Orestes Leal Rodriguez:
>>> Use the force^Wcheckpatch.pl.
>> This is the output of checkpatch.pl:
>> output of checkpatch: total: 0 errors, 0 warnings, 42 lines checked
>> /root/string.c.patch has no obvious style problems and is ready for
>> submission
>
> But it does not apply at all.
> Did you test it? I fear your mail client did some whitespace damage.
yes, I patched my original source tree with it.
>
>>> You need to explain that in the commit message, my young padawan.
>> Very small update to strlen and strnlen that now use less cpu instructions
>> by using a counter to avoid memory address
>> arithmetic, which cause that the compiler adds more machine
>> instructions for computing the length of the string just before
>> returning from the functions, the old machine code is like the
>> following:
>>
>> mov -0x4(%ebp),%edx
>> mov 0x8(%ebp),%eax
>> sub %eax,%edx
>> mov %edx,%eax
>> leave
>> ret
>>
>>
>> now in the new versions the value is not calculated anymore,
>> instead he value of the counter is put on eax after the
>> condition inside the loop no longer holds, and then return:
>>
>> mov -0x4(%ebp),%eax
>> leave
>> ret
>>
>> With this a few cpu instructions are saved.
>
> x86_32 does not matter here as we have already an optimized strlen() in
> arch/x86/lib/string_32.c.
> Did you check whether the optimization is worth on other archs?
> Hint: grep __HAVE_ARCH_STRLEN
I only have access to x86 cpus, but thanks for the hint
>
>>
>> Signed-off-by: Orestes Leal Rodriguez <lukes357@gmail.com>
>> ---
>>
>> Signed-off-by: Orestes Leal Rodriguez <lukes357@gmail.com>
>
> What does this 2nd SoB here?
Again, confusion about where to put the sob.
>
>> diff --git a/lib/string.c b/lib/string.c
>> index 992bf30..c873436 100644
>> --- a/lib/string.c
>> +++ b/lib/string.c
>> @@ -17,6 +17,10 @@
>> * * Sat Feb 09 2002, Jason Thomas <jason@topic.com.au>,
>> * Matthew Hawkins <matt@mh.dropbear.id.au>
>> * - Kissed strtok() goodbye
>> + *
>> + * * Tuesday June 16 2015, Orestes Leal Rodriguez <lukes357@gmail.com>
>> + * - strlen, strnlen: by using a single counter we use less cpu
>> instructions
>> + * by avoiding substracting the memory addresses before return
>
> No need to add anything here. These days we have git. :-)
Ups!
>
>> */
>>
>> #include <linux/types.h>
>> @@ -401,11 +405,11 @@ EXPORT_SYMBOL(strim);
>> */
>> size_t strlen(const char *s)
>> {
>> - const char *sc;
>> + size_t sz = 0;
>>
>> - for (sc = s; *sc != '\0'; ++sc)
>> - /* nothing */;
>> - return sc - s;
>> + for (; *s++ != '\0'; sz++)
>> + /* empty */;
>
> <nitpick>
> Why suddenly "empty" instead of "nothing"?
> </nitpick>
I was bored.
>
>> + return sz;
>> }
>> EXPORT_SYMBOL(strlen);
>> #endif
>> @@ -418,12 +422,13 @@ EXPORT_SYMBOL(strlen);
>> */
>> size_t strnlen(const char *s, size_t count)
>> {
>> - const char *sc;
>> + size_t sz = 0;
>>
>> - for (sc = s; count-- && *sc != '\0'; ++sc)
>> - /* nothing */;
>> - return sc - s;
>> + for (; count-- && *s++ != '\0'; sz++)
>> + /* empty */;
>
> Same here.
>
> Thanks,
> //R2D2
>
Thanks to you richard.
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH 1/1] lib: small update for strlen, strnlen, use less cpu instructions
2015-06-16 22:51 Orestes Leal Rodriguez
@ 2015-06-17 20:07 ` Richard Weinberger
2015-06-19 3:11 ` Orestes Leal Rodriguez
0 siblings, 1 reply; 6+ messages in thread
From: Richard Weinberger @ 2015-06-17 20:07 UTC (permalink / raw)
To: Orestes Leal Rodriguez, bp; +Cc: linux-kernel
Am 17.06.2015 um 00:51 schrieb Orestes Leal Rodriguez:
>> Use the force^Wcheckpatch.pl.
> This is the output of checkpatch.pl:
> output of checkpatch: total: 0 errors, 0 warnings, 42 lines checked
> /root/string.c.patch has no obvious style problems and is ready for submission
But it does not apply at all.
Did you test it? I fear your mail client did some whitespace damage.
>> You need to explain that in the commit message, my young padawan.
> Very small update to strlen and strnlen that now use less cpu instructions by using a counter to avoid memory address
> arithmetic, which cause that the compiler adds more machine
> instructions for computing the length of the string just before
> returning from the functions, the old machine code is like the
> following:
>
> mov -0x4(%ebp),%edx
> mov 0x8(%ebp),%eax
> sub %eax,%edx
> mov %edx,%eax
> leave
> ret
>
>
> now in the new versions the value is not calculated anymore,
> instead he value of the counter is put on eax after the
> condition inside the loop no longer holds, and then return:
>
> mov -0x4(%ebp),%eax
> leave
> ret
>
> With this a few cpu instructions are saved.
x86_32 does not matter here as we have already an optimized strlen() in
arch/x86/lib/string_32.c.
Did you check whether the optimization is worth on other archs?
Hint: grep __HAVE_ARCH_STRLEN
>
> Signed-off-by: Orestes Leal Rodriguez <lukes357@gmail.com>
> ---
>
> Signed-off-by: Orestes Leal Rodriguez <lukes357@gmail.com>
What does this 2nd SoB here?
> diff --git a/lib/string.c b/lib/string.c
> index 992bf30..c873436 100644
> --- a/lib/string.c
> +++ b/lib/string.c
> @@ -17,6 +17,10 @@
> * * Sat Feb 09 2002, Jason Thomas <jason@topic.com.au>,
> * Matthew Hawkins <matt@mh.dropbear.id.au>
> * - Kissed strtok() goodbye
> + *
> + * * Tuesday June 16 2015, Orestes Leal Rodriguez <lukes357@gmail.com>
> + * - strlen, strnlen: by using a single counter we use less cpu instructions
> + * by avoiding substracting the memory addresses before return
No need to add anything here. These days we have git. :-)
> */
>
> #include <linux/types.h>
> @@ -401,11 +405,11 @@ EXPORT_SYMBOL(strim);
> */
> size_t strlen(const char *s)
> {
> - const char *sc;
> + size_t sz = 0;
>
> - for (sc = s; *sc != '\0'; ++sc)
> - /* nothing */;
> - return sc - s;
> + for (; *s++ != '\0'; sz++)
> + /* empty */;
<nitpick>
Why suddenly "empty" instead of "nothing"?
</nitpick>
> + return sz;
> }
> EXPORT_SYMBOL(strlen);
> #endif
> @@ -418,12 +422,13 @@ EXPORT_SYMBOL(strlen);
> */
> size_t strnlen(const char *s, size_t count)
> {
> - const char *sc;
> + size_t sz = 0;
>
> - for (sc = s; count-- && *sc != '\0'; ++sc)
> - /* nothing */;
> - return sc - s;
> + for (; count-- && *s++ != '\0'; sz++)
> + /* empty */;
Same here.
Thanks,
//R2D2
^ permalink raw reply [flat|nested] 6+ messages in thread
* [PATCH 1/1] lib: small update for strlen, strnlen, use less cpu instructions
@ 2015-06-16 22:51 Orestes Leal Rodriguez
2015-06-17 20:07 ` Richard Weinberger
0 siblings, 1 reply; 6+ messages in thread
From: Orestes Leal Rodriguez @ 2015-06-16 22:51 UTC (permalink / raw)
To: bp; +Cc: richard.weinberger, linux-kernel
> Use the force^Wcheckpatch.pl.
This is the output of checkpatch.pl:
output of checkpatch: total: 0 errors, 0 warnings, 42 lines checked
/root/string.c.patch has no obvious style problems and is ready for
submission
> You need to explain that in the commit message, my young padawan.
Very small update to strlen and strnlen that now use less cpu
instructions by using a counter to avoid memory address
arithmetic, which cause that the compiler adds more machine
instructions for computing the length of the string just before
returning from the functions, the old machine code is like the
following:
mov -0x4(%ebp),%edx
mov 0x8(%ebp),%eax
sub %eax,%edx
mov %edx,%eax
leave
ret
now in the new versions the value is not calculated anymore,
instead he value of the counter is put on eax after the
condition inside the loop no longer holds, and then return:
mov -0x4(%ebp),%eax
leave
ret
With this a few cpu instructions are saved.
Signed-off-by: Orestes Leal Rodriguez <lukes357@gmail.com>
---
Signed-off-by: Orestes Leal Rodriguez <lukes357@gmail.com>
diff --git a/lib/string.c b/lib/string.c
index 992bf30..c873436 100644
--- a/lib/string.c
+++ b/lib/string.c
@@ -17,6 +17,10 @@
* * Sat Feb 09 2002, Jason Thomas <jason@topic.com.au>,
* Matthew Hawkins <matt@mh.dropbear.id.au>
* - Kissed strtok() goodbye
+ *
+ * * Tuesday June 16 2015, Orestes Leal Rodriguez <lukes357@gmail.com>
+ * - strlen, strnlen: by using a single counter we use less cpu
instructions
+ * by avoiding substracting the memory addresses before return
*/
#include <linux/types.h>
@@ -401,11 +405,11 @@ EXPORT_SYMBOL(strim);
*/
size_t strlen(const char *s)
{
- const char *sc;
+ size_t sz = 0;
- for (sc = s; *sc != '\0'; ++sc)
- /* nothing */;
- return sc - s;
+ for (; *s++ != '\0'; sz++)
+ /* empty */;
+ return sz;
}
EXPORT_SYMBOL(strlen);
#endif
@@ -418,12 +422,13 @@ EXPORT_SYMBOL(strlen);
*/
size_t strnlen(const char *s, size_t count)
{
- const char *sc;
+ size_t sz = 0;
- for (sc = s; count-- && *sc != '\0'; ++sc)
- /* nothing */;
- return sc - s;
+ for (; count-- && *s++ != '\0'; sz++)
+ /* empty */;
+ return sz;
}
+
EXPORT_SYMBOL(strnlen);
#endif
^ permalink raw reply related [flat|nested] 6+ messages in thread
* Re: [PATCH 1/1] lib: small update for strlen, strnlen, use less cpu instructions
2015-06-16 18:50 Orestes Leal Rodriguez
@ 2015-06-16 22:16 ` Joe Perches
0 siblings, 0 replies; 6+ messages in thread
From: Joe Perches @ 2015-06-16 22:16 UTC (permalink / raw)
To: Orestes Leal Rodriguez; +Cc: linux-kernel, mihai.dontu
On Tue, 2015-06-16 at 13:50 -0500, Orestes Leal Rodriguez wrote:
> Very small update to strlen and strnlen that now use less cpu
> instructions by using a counter to avoid the memory addresses
> substraction to find the length of the string.
[]
> @@ -418,12 +422,13 @@ EXPORT_SYMBOL(strlen);
> */
> size_t strnlen(const char *s, size_t count)
> {
> - const char *sc;
> + size_t sz = 0;
>
> - for (sc = s; count-- && *sc != '\0'; ++sc)
> - /* nothing */;
> - return sc - s;
> + for (; count-- && *s++ != '\0'; sz++)
> + /* empty */;
> + return sz;
That's one subtraction at end-of-string vs
a register increment for each non-zero byte.
smaller isn't worth slower.
^ permalink raw reply [flat|nested] 6+ messages in thread
* [PATCH 1/1] lib: small update for strlen, strnlen, use less cpu instructions
@ 2015-06-16 18:50 Orestes Leal Rodriguez
2015-06-16 22:16 ` Joe Perches
0 siblings, 1 reply; 6+ messages in thread
From: Orestes Leal Rodriguez @ 2015-06-16 18:50 UTC (permalink / raw)
To: linux-kernel; +Cc: mihai.dontu
Very small update to strlen and strnlen that now use less cpu
instructions by using a counter to avoid the memory addresses
substraction to find the length of the string.
Signed-off-by: Orestes Leal Rodriguez <lukes357@gmail.com>
---
diff --git a/lib/string.c" "b/lib/string.c
index 992bf30..c873436 100644
--- a/lib/string.c
+++ b/lib/string.c
@@ -17,6 +17,10 @@
* * Sat Feb 09 2002, Jason Thomas <jason@topic.com.au>,
* Matthew Hawkins <matt@mh.dropbear.id.au>
* - Kissed strtok() goodbye
+ *
+ * * Tuesday June 16 2015, Orestes Leal Rodriguez <lukes357@gmail.com>
+ * - strlen, strnlen: by using a single counter we use less cpu
instructions
+ * by avoiding substracting the memory addresses before return
*/
#include <linux/types.h>
@@ -401,11 +405,11 @@ EXPORT_SYMBOL(strim);
*/
size_t strlen(const char *s)
{
- const char *sc;
+ size_t sz = 0;
- for (sc = s; *sc != '\0'; ++sc)
- /* nothing */;
- return sc - s;
+ for (; *s++ != '\0'; sz++)
+ /* empty */;
+ return sz;
}
EXPORT_SYMBOL(strlen);
#endif
@@ -418,12 +422,13 @@ EXPORT_SYMBOL(strlen);
*/
size_t strnlen(const char *s, size_t count)
{
- const char *sc;
+ size_t sz = 0;
- for (sc = s; count-- && *sc != '\0'; ++sc)
- /* nothing */;
- return sc - s;
+ for (; count-- && *s++ != '\0'; sz++)
+ /* empty */;
+ return sz;
}
+
EXPORT_SYMBOL(strnlen);
#endif
^ permalink raw reply related [flat|nested] 6+ messages in thread
end of thread, other threads:[~2015-06-19 3:11 UTC | newest]
Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2015-06-16 18:51 [PATCH 1/1] lib: small update for strlen, strnlen, use less cpu instructions Orestes Leal Rodriguez
-- strict thread matches above, loose matches on Subject: below --
2015-06-16 22:51 Orestes Leal Rodriguez
2015-06-17 20:07 ` Richard Weinberger
2015-06-19 3:11 ` Orestes Leal Rodriguez
2015-06-16 18:50 Orestes Leal Rodriguez
2015-06-16 22:16 ` Joe Perches
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.