Date: Fri, 24 Mar 2000 21:27:57 -0800 (PST) From: Matthew Dillon <dillon@apollo.backplane.com> To: Alfred Perlstein <bright@wintelcom.net>, freebsd-current@FreeBSD.ORG Subject: Why are all accesses to the cpl surrounded by a lock? Message-ID: <200003250527.VAA19096@apollo.backplane.com>
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I've been doing more SMP cleanup and for the life of me I can't figure
out why cpl operations are surrounded by its own [S]CPL_LOCK ??
As far as I can tell, the cpl is only accessed/modified:
* by mainline code while the MP lock is held
* by an interrupt while the MP lock is held
Since any modification of the cpl within an interrupt is paired and
thus from the point of view of mainline code the cpl does not change
at all (i.e. s = splvm(); ... splx(s);), I don't see why the cpl needs
to be locked at all. We shouldn't even need to use a 'lock' prefix.
Now, I understand that we eventually want to get out from under the MP
lock's thumb, but it needs to be pointed out that the cpl mechanism
itself is likely to be depreciated in favor of something more
thread-friendly. I don't see any point in trying to make the cpl
operate independantly of the MP lock at this time.
Does anyone know why all the locking was added to the cpl code?
-Matt
Matthew Dillon
<dillon@backplane.com>
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