On Sat, 29 Jan 2005, Brian Gerst wrote: > Jesper Juhl wrote: > > In kernel/params.c::module_attr_show and kernel/params.c::module_attr_store > > we call to_module_kobject() and save the result in a local variable right > > before a conditional statement that does not depend on the call to > > to_module_kobject() and may cause the function to return. If the function > > returns before we use the result of to_module_kobject() then the call is > > just a waste of time. The patch moves the call to to_module_kobject() down > > just before it is actually used, thus we save a call to the function in a > > few cases. I doubt this is in any way measurable, but I see no reason to not > > move the call - it should be an infinitesimal improvement with no ill > > sideeffects. > > Please consider applying. > > > > > > Signed-off-by: Jesper Juhl <[EMAIL PROTECTED]> > > > > diff -up linux-2.6.11-rc2-bk7-orig/kernel/params.c > > linux-2.6.11-rc2-bk7/kernel/params.c > > --- linux-2.6.11-rc2-bk7-orig/kernel/params.c 2005-01-29 > > 23:54:53.000000000 > > +0100 > > +++ linux-2.6.11-rc2-bk7/kernel/params.c 2005-01-30 00:27:08.000000000 > > +0100 > > @@ -625,11 +625,12 @@ static ssize_t module_attr_show(struct k > > int ret; > > attribute = to_module_attr(attr); > > - mk = to_module_kobject(kobj); > > if (!attribute->show) > > return -EPERM; > > + mk = to_module_kobject(kobj); > > + > > if (!try_module_get(mk->mod)) > > return -ENODEV; > > @@ -649,11 +650,12 @@ static ssize_t module_attr_store(struct int > > ret; > > attribute = to_module_attr(attr); > > - mk = to_module_kobject(kobj); > > if (!attribute->store) > > return -EPERM; > > + mk = to_module_kobject(kobj); > > + > > if (!try_module_get(mk->mod)) > > return -ENODEV; > > > > > > I'd bet that the compiler already reorders the assignment since there is no > side effect to to_module_kobject(). Even with a patch like this you can't > control exactly when the assignment is done. There may not even be an > assignment, since mk is a constant offset of kobj. > True, the compiler is free to be clever, but I still think it's best to write the code in the most optimal way as seen from a C perspective. I just took a look at the compiled object files with and without the patch, and it makes no difference what-so-ever - gcc generates the exact same code. So you are right, gcc is clever about it. Hmm, it's Rusty's code as far as I can see, I'll leave it up to him to apply the patch or not.
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