Re: [PATCH 2/5] vmevent: Convert from deferred timer to deferred work

[KOSAKI Motohiro <kosaki.motohiro@gmail.com>]

(6/1/12 8:24 AM), Anton Vorontsov wrote:
> We'll need to use smp_function_call() in the sampling routines, and the
> call is not supposed to be called from the bottom halves. So, let's
> convert vmevent to dffered workqueues.
> 
> As a side effect, we also fix the swap reporting (we cannot call
> si_swapinfo from the interrupt context), i.e. the following oops should
> be fixed now:
> 
>   =================================
>   [ INFO: inconsistent lock state ]
>   3.4.0-rc1+ #37 Not tainted
>   ---------------------------------
>   inconsistent {SOFTIRQ-ON-W} ->  {IN-SOFTIRQ-W} usage.
>   swapper/0/0 [HC0[0]:SC1[1]:HE1:SE0] takes:
>    (swap_lock){+.?...}, at: [<ffffffff8110449d>] si_swapinfo+0x1d/0x90
>   {SOFTIRQ-ON-W} state was registered at:
>     [<ffffffff8107ca7f>] mark_irqflags+0x15f/0x1b0
>     [<ffffffff8107e5e3>] __lock_acquire+0x493/0x9d0
>     [<ffffffff8107f20e>] lock_acquire+0x9e/0x200
>     [<ffffffff813e9071>] _raw_spin_lock+0x41/0x50
>     [<ffffffff8110449d>] si_swapinfo+0x1d/0x90
>     [<ffffffff8117e7c8>] meminfo_proc_show+0x38/0x3f0
>     [<ffffffff81141209>] seq_read+0x139/0x3f0
>     [<ffffffff81174cc6>] proc_reg_read+0x86/0xc0
>     [<ffffffff8111c19c>] vfs_read+0xac/0x160
>     [<ffffffff8111c29a>] sys_read+0x4a/0x90
>     [<ffffffff813ea652>] system_call_fastpath+0x16/0x1b
> 
> Signed-off-by: Anton Vorontsov<anton.vorontsov@linaro.org>

As I already told you, vmevent shouldn't deal a timer at all. It is
NOT familiar to embedded world. Because of, time subsystem is one of
most complex one on linux. Our 'time' is not simple concept. time.h
says we have 5 possibilities user want, at least.

include/linux/time.h
------------------------------------------
#define CLOCK_REALTIME			0
#define CLOCK_MONOTONIC			1
#define CLOCK_MONOTONIC_RAW		4
#define CLOCK_REALTIME_COARSE		5
#define CLOCK_MONOTONIC_COARSE		6

And, some people want to change timer slack for optimize power 
consumption.

So, Don't reinventing the wheel. Just use posix tiemr apis.