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    SubjectRe: [patch] Real-Time Preemption, -RT-2.6.13-rc4-V0.7.52-01
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    Date
    On Fri, 2005-08-26 at 08:08 +0200, Ingo Molnar wrote:
    > * Steven Rostedt <rostedt@goodmis.org> wrote:
    >
    > > So, the only other solutions that I can think of is:
    > >
    > > a) add yet another (bloat) lock to the buffer head.
    > >
    > > b) Still use your b_update_lock for the jbd_lock_bh_journal_head and
    > > change the jbd_lock_bh_state to what I discussed earlier, and that
    > > being the hash wait_on_bit code.
    >
    > could you try a), how clean does it get? Personally i'm much more in
    > favor of cleanliness. On the vanilla kernel a spinlock is zero bytes on
    > UP [the most RAM-sensitive platform], and it's a word on typical SMP.

    Not only the cleanest, but also the simplest :-)

    -- Steve

    Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

    Index: linux_realtime_ernie/fs/buffer.c
    ===================================================================
    --- linux_realtime_ernie/fs/buffer.c (revision 303)
    +++ linux_realtime_ernie/fs/buffer.c (working copy)
    @@ -3053,6 +3053,7 @@
    {
    BUG_ON(!list_empty(&bh->b_assoc_buffers));
    BUG_ON(spin_is_locked(&bh->b_uptodate_lock));
    + BUG_ON(spin_is_locked(&bh->b_state_lock));
    kmem_cache_free(bh_cachep, bh);
    preempt_disable();
    __get_cpu_var(bh_accounting).nr--;
    @@ -3071,6 +3072,7 @@
    memset(bh, 0, sizeof(*bh));
    INIT_LIST_HEAD(&bh->b_assoc_buffers);
    spin_lock_init(&bh->b_uptodate_lock);
    + spin_lock_init(&bh->b_state_lock);
    }
    }

    Index: linux_realtime_ernie/include/linux/buffer_head.h
    ===================================================================
    --- linux_realtime_ernie/include/linux/buffer_head.h (revision 303)
    +++ linux_realtime_ernie/include/linux/buffer_head.h (working copy)
    @@ -62,6 +62,7 @@
    void *b_private; /* reserved for b_end_io */
    struct list_head b_assoc_buffers; /* associated with another mapping */
    spinlock_t b_uptodate_lock;
    + spinlock_t b_state_lock;
    };

    /*
    Index: linux_realtime_ernie/include/linux/jbd.h
    ===================================================================
    --- linux_realtime_ernie/include/linux/jbd.h (revision 303)
    +++ linux_realtime_ernie/include/linux/jbd.h (working copy)
    @@ -326,32 +326,32 @@

    static inline void jbd_lock_bh_state(struct buffer_head *bh)
    {
    - bit_spin_lock(BH_State, &bh->b_state);
    + spin_lock(&bh->b_state_lock);
    }

    static inline int jbd_trylock_bh_state(struct buffer_head *bh)
    {
    - return bit_spin_trylock(BH_State, &bh->b_state);
    + return spin_trylock(&bh->b_state_lock);
    }

    static inline int jbd_is_locked_bh_state(struct buffer_head *bh)
    {
    - return bit_spin_is_locked(BH_State, &bh->b_state);
    + return spin_is_locked(&bh->b_state_lock);
    }

    static inline void jbd_unlock_bh_state(struct buffer_head *bh)
    {
    - bit_spin_unlock(BH_State, &bh->b_state);
    + spin_unlock(&bh->b_state_lock);
    }

    static inline void jbd_lock_bh_journal_head(struct buffer_head *bh)
    {
    - bit_spin_lock(BH_JournalHead, &bh->b_state);
    + spin_lock(&bh->b_uptodate_lock);
    }

    static inline void jbd_unlock_bh_journal_head(struct buffer_head *bh)
    {
    - bit_spin_unlock(BH_JournalHead, &bh->b_state);
    + spin_unlock(&bh->b_uptodate_lock);
    }

    struct jbd_revoke_table_s;

    -
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