linux-kernel - Re: [PATCH v7 06/16] tracepoint: use new hashtable implementation

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Message-ID: <20121029175007.GA20796@Krystal>
Date:	Mon, 29 Oct 2012 13:50:07 -0400
From:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:	Sasha Levin <levinsasha928@...il.com>
Cc:	torvalds@...ux-foundation.org, tj@...nel.org,
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Subject: Re: [PATCH v7 06/16] tracepoint: use new hashtable implementation

* Sasha Levin (levinsasha928@...il.com) wrote:
> On Mon, Oct 29, 2012 at 7:35 AM, Mathieu Desnoyers
> <mathieu.desnoyers@...icios.com> wrote:
> > * Sasha Levin (levinsasha928@...il.com) wrote:
> >> Switch tracepoints to use the new hashtable implementation. This reduces the amount of
> >> generic unrelated code in the tracepoints.
> >>
> >> Signed-off-by: Sasha Levin <levinsasha928@...il.com>
> >> ---
> >>  kernel/tracepoint.c | 27 +++++++++++----------------
> >>  1 file changed, 11 insertions(+), 16 deletions(-)
> >>
> >> diff --git a/kernel/tracepoint.c b/kernel/tracepoint.c
> >> index d96ba22..854df92 100644
> >> --- a/kernel/tracepoint.c
> >> +++ b/kernel/tracepoint.c
> >> @@ -26,6 +26,7 @@
> >>  #include <linux/slab.h>
> >>  #include <linux/sched.h>
> >>  #include <linux/static_key.h>
> >> +#include <linux/hashtable.h>
> >>
> >>  extern struct tracepoint * const __start___tracepoints_ptrs[];
> >>  extern struct tracepoint * const __stop___tracepoints_ptrs[];
> >> @@ -49,8 +50,7 @@ static LIST_HEAD(tracepoint_module_list);
> >>   * Protected by tracepoints_mutex.
> >>   */
> >>  #define TRACEPOINT_HASH_BITS 6
> >> -#define TRACEPOINT_TABLE_SIZE (1 << TRACEPOINT_HASH_BITS)
> >> -static struct hlist_head tracepoint_table[TRACEPOINT_TABLE_SIZE];
> >> +static DEFINE_HASHTABLE(tracepoint_table, TRACEPOINT_HASH_BITS);
> >>
> > [...]
> >>
> >> @@ -722,6 +715,8 @@ struct notifier_block tracepoint_module_nb = {
> >>
> >>  static int init_tracepoints(void)
> >>  {
> >> +     hash_init(tracepoint_table);
> >> +
> >>       return register_module_notifier(&tracepoint_module_nb);
> >>  }
> >>  __initcall(init_tracepoints);
> >
> > So we have a hash table defined in .bss (therefore entirely initialized
> > to NULL), and you add a call to "hash_init", which iterates on the whole
> > array and initialize it to NULL (again) ?
> >
> > This extra initialization is redundant. I think it should be removed
> > from here, and hashtable.h should document that hash_init() don't need
> > to be called on zeroed memory (which includes static/global variables,
> > kzalloc'd memory, etc).
> 
> This was discussed in the previous series, the conclusion was to call
> hash_init() either way to keep the encapsulation and consistency.

Agreed,

Thanks,

Mathieu

> 
> It's cheap enough and happens only once, so why not?
> 
> 
> Thanks,
> Sasha

-- 
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com
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