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    SubjectRe: [patch] lockless, scalable get_pid(), for_each_process() elimination, 2.5.35-BK
    On Wed, Sep 18, 2002 at 12:11:30PM +0200, Ingo Molnar wrote:
    > so i think the most we could get is to actually eliminate the pidhash and
    > use the idtag hash for it. This would concentrate all the performance
    > efforts on the idtag hash.

    I eventually had special-case handling of IDTAG_PID so that it did not
    use idtags, but chained tasks directly, and removing the pidhash as goals.

    On Wed, Sep 18, 2002 at 12:11:30PM +0200, Ingo Molnar wrote:
    > another, locking improvement is possible as well:
    > - the idtag spinlock should be eliminated, we can reuse the tasklist lock
    > for it - in the exit and fork path we hold it already. This also means
    > we can walk an ID list by read-locking the tasklist lock.
    > the idtag spinlock is already superfluous i think, because the idtag task
    > list is only safely walked if we read-lock the task list. So it's not like
    > anyone could hash in a new idtag while we walk the list.
    > What do you think?

    ISTR the idtag_lock was for cases where the hashtable was modified
    while the tasklist_lock was only held for reading. Basically, once
    those are resolved, the idtag_lock goes away.

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