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Date: Wed, 18 Sep 2002 07:28:23 -0700
From: William Lee Irwin III <wli@holomorphy.com>
To: Ingo Molnar <mingo@elte.hu>
Cc: Linus Torvalds <torvalds@transmeta.com>, linux-kernel@vger.kernel.org
Subject: Re: [patch] lockless, scalable get_pid(), for_each_process() elimination, 2.5.35-BK
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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.


Cheers,
Bill
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