Re: [RFC patch] spindep: add cross cache lines checking

[Alex Shi <alex.shi@intel.com>]

Resend for correct tglx's address. Sorry!
> > > 
> > > Have you tried making this a compile-time check using 
> > > __alignof__? I would say that any spinlock in a packed data 
> > > structure is basically a bug, even more so on most other 
> > > architectures besides x86.
> 
> I have one concern and one questions here:
> concern: maybe the lock is in a well designed 'packed' struct, and it is
> safe for cross lines issue. but __alignof__ will return 1;
> 
> struct abc{
> 	raw_spinlock_t lock1;
> 	char 		a;
> 	char		b;
> }__attribute__((packed));
> 
> Since the lock is the first object of struct, usually it is well placed.
> 
> question: I am a idiot on gcc, I tried some parameters of gcc " --param
> l1-cache-line-size=1  -mno-align-double" and can not make a cross lines
> variable without 'packed' structure, but I still don't find a grantee
> why gcc can avoid the cross line variable if it's not in 'packed'
> structure? 
> 
> > agreed.
> > 
> > Thanks,
> > 
> > 	Ingo
>