Hi,
There are a lot of places in the kernel where we dereference several pointers
in a row several times.
As far as I can tell it should be more efficient to just deref those pointers
once, store the result in a variable, and then use that (unless the use is very
limited of course).
To "test the waters" before I do a lot of work that won't be accepted, I picked
a random file with generic kernel code that has this issue and made a patch.
What I'd like to know is if anyone sees any problems with this and if patches
such as this one would be considered a good thing.
If patches like the one below are wanted I'll have a bunch of similar ones
ready to go pretty soon.
I've compile tested this patch and I'm currently running a 2.6.15-rc5-git1
kernel with it applied without problems.
Ohh, and before I forget, besides the fact that this should speed things up a
little bit it also has the added benefit of reducing the size of the generated
code.
The original kernel/exit.o file was 19604 bytes in size, the patched one is
19508 bytes in size.
Comments very welcome.
Signed-off-by: Jesper Juhl <[email protected]>
---
kernel/exit.c | 37 +++++++++++++++++++++----------------
1 files changed, 21 insertions(+), 16 deletions(-)
--- linux-2.6.15-rc5-git1-orig/kernel/exit.c 2005-12-04 18:48:53.000000000 +0100
+++ linux-2.6.15-rc5-git1/kernel/exit.c 2005-12-06 22:11:17.000000000 +0100
@@ -1068,6 +1068,9 @@ static int wait_task_zombie(task_t *p, i
}
if (likely(p->real_parent == p->parent) && likely(p->signal)) {
+ struct signal_struct *psig;
+ struct signal_struct *sig;
+
/*
* The resource counters for the group leader are in its
* own task_struct. Those for dead threads in the group
@@ -1084,24 +1087,26 @@ static int wait_task_zombie(task_t *p, i
* here reaping other children at the same time.
*/
spin_lock_irq(&p->parent->sighand->siglock);
- p->parent->signal->cutime =
- cputime_add(p->parent->signal->cutime,
+ psig = p->parent->signal;
+ sig = p->signal;
+ psig->cutime =
+ cputime_add(psig->cutime,
cputime_add(p->utime,
- cputime_add(p->signal->utime,
- p->signal->cutime)));
- p->parent->signal->cstime =
- cputime_add(p->parent->signal->cstime,
+ cputime_add(sig->utime,
+ sig->cutime)));
+ psig->cstime =
+ cputime_add(psig->cstime,
cputime_add(p->stime,
- cputime_add(p->signal->stime,
- p->signal->cstime)));
- p->parent->signal->cmin_flt +=
- p->min_flt + p->signal->min_flt + p->signal->cmin_flt;
- p->parent->signal->cmaj_flt +=
- p->maj_flt + p->signal->maj_flt + p->signal->cmaj_flt;
- p->parent->signal->cnvcsw +=
- p->nvcsw + p->signal->nvcsw + p->signal->cnvcsw;
- p->parent->signal->cnivcsw +=
- p->nivcsw + p->signal->nivcsw + p->signal->cnivcsw;
+ cputime_add(sig->stime,
+ sig->cstime)));
+ psig->cmin_flt +=
+ p->min_flt + sig->min_flt + sig->cmin_flt;
+ psig->cmaj_flt +=
+ p->maj_flt + sig->maj_flt + sig->cmaj_flt;
+ psig->cnvcsw +=
+ p->nvcsw + sig->nvcsw + sig->cnvcsw;
+ psig->cnivcsw +=
+ p->nivcsw + sig->nivcsw + sig->cnivcsw;
spin_unlock_irq(&p->parent->sighand->siglock);
}
--
Jesper Juhl <[email protected]>
Don't top-post http://www.catb.org/~esr/jargon/html/T/top-post.html
Plain text mails only, please http://www.expita.com/nomime.html
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