• Stefan Richter's avatar
    ieee1394: shrink tlabel pools, remove tpool semaphores · 9951903e
    Stefan Richter authored
    This patch reduces the size of struct hpsb_host and also removes
    semaphores from ieee1394_transactions.c.  On i386, struct hpsb_host
    shrinks from 10656 bytes to 6688 bytes.  This is accomplished by
     - using a single wait_queue for hpsb_get_tlabel instead of many
       instances of semaphores,
     - using a single lock to serialize access to all tlabel pools (the
       protected code regions are small, i.e. lock contention very low),
     - omitting the sysfs attribute tlabels_allocations.
    Drawback:  In the rare case that a process needs to sleep because all
    transaction labels for the node are temporarily exhausted, it is also
    woken up if a tlabel for a different node became free, checks for an
    available tlabel, and is put to sleep again.  The check is not costly
    and the situation occurs extremely rarely.  (Tlabels are typically
    only exhausted if there was no context switch to the khpsbpkt thread
    which recycles tlables.)  Therefore the benefit of reduced tpool size
    outweighs this drawback.
    The sysfs attributes tlabels_free and tlabels_mask are not compiled
    anymore unless CONFIG_IEEE1394_VERBOSEDEBUG is set.
    The by far biggest member of struct hpsb_host, the struct csr_control
    csr (5272 bytes on i386), is now placed at the end of struct hpsb_host.
    Note, hpsb_get_tlabel calls the macro wait_event_interruptible with a
    condition argument which has a side effect (allocation of a tlabel and
    manipulation of the packet).  This side effect happens only if the
    condition is true.  The patch relies on wait_event_interruptible not
    evaluating the condition again after it became true.
    Signed-off-by: default avatarStefan Richter <stefanr@s5r6.in-berlin.de>