lkml.org 
[lkml]   [2010]   [Apr]   [10]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: Question about lock sequence
From
Date
On Sat, 2010-04-10 at 19:44 +0900, Hitoshi Mitake wrote:
> Hi,
>
> I found that my understand about lockdep is completely wrong :( ,
> so state machine of perf lock should be fixed before optimization.
>
> And I found that behaviour related to some of spin locks are strange.
> The concrete example is lock sequences targeting dcache_lock (defined in
> head of fs/dcache.c).
>
> I made a little (and not essential) change to perf lock, and observe
> lock sequence targeting it.
> Changed perf lock shows sequence of locks in time order,
> and I grepped the output of it with dcache, like this:
>
> % sudo ./perf lock report | grep dcache
>
> The head part of result is this:
> # <name>-<pid> <time (in u64)> <action> <address of lockdep> <name of lock>
> perf-3238 92430534170 acquire: 0xffffffff81a4b398 dcache_lock
> perf-3238 92430536714 acquire: 0xffffffff81a4b398 dcache_lock
> perf-3238 92431444481 acquire: 0xffffffff81a4b398 dcache_lock
> perf-3238 92431446061 acquired: 0xffffffff81a4b398 dcache_lock
> perf-3238 92431448157 acquire: 0xffffffff81a4b398 dcache_lock
> perf-3238 92431449670 acquired: 0xffffffff81a4b398 dcache_lock
> perf-3238 92432371136 acquire: 0xffffffff81a4b398 dcache_lock
> perf-3238 92432372712 acquired: 0xffffffff81a4b398 dcache_lock
> perf-3238 92432374718 acquire: 0xffffffff81a4b398 dcache_lock
> perf-3238 92432376173 acquired: 0xffffffff81a4b398 dcache_lock
> perf-3238 92433315563 acquire: 0xffffffff81a4b398 dcache_lock
> perf-3238 92433317173 acquired: 0xffffffff81a4b398 dcache_lock
>
> There are too many acquire and acquired without corresponding release
> (or contended).
> If dcache_lock is rwlock and these acquires mean read locks, this is not
> so strange.
> But, for me, this is a pattern of dead lock.
> Of course perf lock finished its work, so there is no actual dead lock.
>
> If you know something about this behaviour of lock, could you tell me?

Well dcache_lock is a regular spinlock and there is only one of them, my
guess is that your timeline got messed up somehow.

Also, there doesn't appear to be a proper balance between acquires and
releases.




\
 
 \ /
  Last update: 2010-04-10 16:03    [from the cache]
©2003-2014 Jasper Spaans. Advertise on this site