Messages in this thread | | | From | "Stephen C. Tweedie" <> | Date | Tue, 27 Jul 1999 06:00:11 +0100 (BST) | Subject | Re: low priority soft RT? |
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Hi,
On Mon, 26 Jul 1999 22:40:25 +0200 (CEST), Rik van Riel <riel@nl.linux.org> said:
> I completely agree on this one. We should probably mark a process > with "bonus" if another process tries to grab a lock that's held > by the first process.
"Priority inheritance." It adds complexity to _every_ place where the kernel blocks. Remember, we don't always use locks. The page cache has a single PG_Locked flag on the page, plus a per-page wait queue. The buffer cache does similar things. Unless you put the extra bonus code into the general-purpose wait queue macros, doing this sort of thing is going to stomp on all sorts of bits of the kernel.
There's a much, much easier way --- just revoke the SCHED_IDLE scheduling class when a process explicitly calls schedule(). That automatically takes care of every single case where a process gives up the CPU from inside the kernel. The only special case then becomes the schedule inside return_to_user, where we want to keep SCHED_IDLE intact.
However, that adds code to two of the hottest paths in the whole kernel. Not nice.
--Stephen
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