lkml.org 
[lkml]   [2010]   [Dec]   [16]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH/RFC 1/2] jump label: make enable/disable o(1)
From
Date
On Thu, 2010-12-16 at 13:25 -0500, Jason Baron wrote:
> Previously, I allowed any variable type to be used as the 'key' for
> the jump label. However, by enforcing a type, we can make use of the
> contents of the 'key'. This patch thus introduces:
>
> struct jump_label_key {
> void *ptr;
> };
>
> The 'ptr' is used a pointer into the jump label table of the
> corresponding addresses that need to be updated. Thus, when jump labels
> are enabled/disabled we have a constant time algorithm. There is no
> longer any hashing.
>
> When jump lables are disabled we simply have:
>
> struct jump_label_key {
> int state;
> };
>
> I've also defined an analogous structure for ref counted jump labels as
> per a request from Peter.
>
> struct jump_label_keyref {
> void *ptr;
> };
>
> And for the jump labels disabled case:
>
>
> struct jump_label_keyref {
> atomic_t refcount;
> };
>
> The reason I've introduced an additional structure for the reference counted
> jump labels is twofold:
>
> 1) For the jump labels disabled case, reference counted jump labels use an
> atomic_read(). I didn't want to impact the jump labels disabled case for
> tracepoints which simply accesses an 'int'.
>
> 2) By introducing a second type, we have two parallel APIs:
>
> extern void jump_label_enable(struct jump_label_key *key);
> extern void jump_label_disable(struct jump_label_key *key);
>
> static inline void jump_label_inc(struct jump_label_keyref *key)
> static inline void jump_label_dec(struct jump_label_keyref *key)
>
> In this way, we can't mix up the reference counted API, with the straight
> enable/disable API since they accept different types.

But why do we want to have two APIs?


\
 
 \ /
  Last update: 2010-12-16 20:13    [W:0.105 / U:0.140 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site