Note that the issue of a "LL" will trigger bus watching activity in the system logic (and maybe delays?) I would personally try to avoid issuing "dangling" ll's in the normal case, even though the functionality would be ok, and in some cases they are inavoidable. /Hartvig Justin Carlson writes: > > On Mon, 2002-02-04 at 23:47, Daniel Jacobowitz wrote: > > > > Won't this cause some gratuitous thrashing if someone else is trying to > > get the spinlock at the same time? > > > > Actually, if you look at the required semantics of ll, no. A ll by > itself can never cause a sc from another cpu to fail. It's part of the > semantic definition to avoid potential livelock cases, e.g. > > A does ll > B does ll, foiling A's lock attempt > A does sc, which fails > A does ll, foiling B's lock attempt > B does sc, which fails > B does ll, foiling A's lock attempt > ... > > Instead, this case becomes: > A does ll > B does ll > A does sc, which succeeds, even though B has done a ll > B does sc which fails > A does critical section work > B spins on ll until A releases the lock > > > -Justin > > -- _ _ _____ ____ Hartvig Ekner Mailto:hartvige@mips.com |\ /| | |____)(____ Direct: +45 4486 5503 | \/ | | | _____) MIPS Denmark Switch: +45 4486 5555 T E C H N O L O G I E S http://www.mips.com Fax...: +45 4486 5556
