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SubjectRe: [RFC][PATCH 1/6] Tunable structure and registration routines
Randy,

Thanks for reviewing the code!
My comments embedded.
I'll re-send the patches as soon as possible.

Regards,
Nadia

Randy Dunlap wrote:
> On Tue, 16 Jan 2007 07:15:17 +0100 Nadia.Derbey@bull.net wrote:
>
>
>>[PATCH 01/06]
>>
<snip>
>
>
>>+Any kernel subsystem that has registered a tunable should call
>>+auto_tune_func() as follows:
>>+
>>++-------------------------+--------------------------------------------+
>>+| Step | Routine to call |
>>++-------------------------+--------------------------------------------+
>>+| Declaration phase | DEFINE_TUNABLE(name, values...); |
>>++-------------------------+--------------------------------------------+
>>+| Initialization routine | set_tunable_min_max(name, min, max); |
>>+| | set_autotuning_routine(name, routine); |
>>+| | register_tunable(&name); |
>>+| Note: the 1st 2 calls | |
>>+| are optional | |
>>++-------------------------+--------------------------------------------+
>>+| Alloc | activate_auto_tuning(AKT_UP, &name); |
>>++-------------------------+--------------------------------------------+
>>+| Free | activate_auto_tuning(AKT_DOWN, &name); |
>
>
> So does Free always use AKT_DOWN? why does it matter?
> Seems unneeded and inconsistent.

Tuning down is recommended in order to come back to the default tunable
value.
I agree with you: today it has quite no effect, except on the tunable
value. If we take the ipc's example, grow_ary() just returns if the new
tunable value happens to be lower than the previous one.
But we can imagine, in the future, that grow_ary could deallocate the
unused memory.
+ in that particular case, lowering the tunable value makes the 1st loop
in ipc_addid() shorter.

> How does one activate a tunable for downward adjustment?

Actually a tunable is activated to be dynamically adjusted (whatever the
direction).
But you are giving me an idea for a future enhancement: we can imagine a
tunable that could be allowed to increase only (or decrease only). In
that case, we should move the autotune sysfs attribute into an 'up' and
a 'down' attribute?

<snip>

>>+
>>+2) User part:
>>+
>>+As seen above, the only way to activate automatic tuning is from user side:
>>+- the directory /sys/tunables is created during the init phase.
>>+- each time a tunable is registered by a kernel subsystem, a directory is
>>+created for it under /sys/tunables.
>>+- This directory contains 1 file for each tunable kobject attribute:
>
>
> Please try to limit text documentation to 80 columns or less.

That's exactly what I did?



<snip>

>>Index: linux-2.6.20-rc4/fs/Kconfig
>>===================================================================
>>--- linux-2.6.20-rc4.orig/fs/Kconfig 2007-01-15 13:08:14.000000000 +0100
>>+++ linux-2.6.20-rc4/fs/Kconfig 2007-01-15 14:20:20.000000000 +0100
>>@@ -925,6 +925,8 @@ config PROC_KCORE
>> bool "/proc/kcore support" if !ARM
>> depends on PROC_FS && MMU
>>
>>+source "kernel/autotune/Kconfig"
>
>
> Why is that is the File systems menu? Seems odd to me
> for it to be there. If it's just because it depends on
> PROC_FS and SYSFS, then it should just go completely after
> the File systems menu.
>

Since the tunables that are handled in AKT, I wanted the feature to be
close to CONFIG_PROC_FS.
Now, I do not agree with your proposal: putting it after the FS menu
means that it would appear in the main menu, right? I'll try to find a
better place for it.



>>Index: linux-2.6.20-rc4/include/linux/akt.h
>>===================================================================
>>--- /dev/null 1970-01-01 00:00:00.000000000 +0000
>>+++ linux-2.6.20-rc4/include/linux/akt.h 2007-01-15 14:26:24.000000000 +0100
>>@@ -0,0 +1,186 @@
>>+


<snip>

>>+ char flags; /* Only 2 bits are meaningful: */
>
>
> Make flags unsigned char so that no sign bit is needed.
>
>
>>+ /* bit 0: set to 1 if the associated tunable can */
>>+ /* be automatically adjusted */
>>+ /* bits 1: set to 1 if the tunable has been */
>>+ /* registered */
>>+ /* bits 2-7: useless */
>
>
> unused ??

yep

<snip>

>
>
>>+
>>+extern void fork_late_init(void);
>
>
> Looks like the wrong header file for that extern.
>
>

Actually, I wanted the changes to the existing kernel files to be as
small as possible. That's why everything is concentrated, whenever
possible, in the added files.

Regards,
Nadia




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