[Lse-tech] [RFC,PATCH] use rcu for fasync_lock

[Manfred S. <ma...@co...>]

Hi,

kill_fasync and fasync_helper were intended for mice and similar, rare 
users, thus it uses a simple rwlock for the locking. This is not true 
anymore: e.g. every pipe read and write operation calls kill_fasync, 
which must acquire the rwlock before handling the fasync list.
What about switching to rcu? I did a reaim run on a 4-way pIII with STP, 
and it reduced the time within kill_fasync by 80%:

diffprofile reaim_End_stock reaim_End_rcu          
     21166     1.2% default_idle
     18882     0.9% total
       290    12.8% page_address
       269    23.5% group_send_sig_info
       259    41.1% do_brk
       244     6.3% current_kernel_time
[ delta < 200: skipped]
      -205   -16.1% get_signal_to_deliver
      -240    -3.7% page_add_rmap
      -364    -4.7% __might_sleep
      -369    -8.4% page_remove_rmap
      -975   -81.2% kill_fasync

What do you think? Patch against 2.6.0 is attached.

--
    Manfred