On Fri, Nov 08, 2002 at 12:05:30PM -0600, Van Maren, Kevin wrote:
> Absolutely you should minimize the locking contention.
> However, that isn't always possible, such as when you
> have 64 processors contending on the same resource.
if you've got 64 processors contending on the same resource, maybe you
need to split that resource up so they can have a copy each. all that
cacheline bouncing can't do your numa boxes any good.
> With the current kernel, the trivial example with reader/
> writer locks was having them all call gettimeofday().
i hear x86-64 has a lockless gettimeofday. maybe that's the solution.
> But try having 64 processors fstat() the same file,
> which I have also seen happen (application looping,
> waiting for another process to finish setting up the
> file so they can all mmap it).
umm.. the call trace:
sys_fstat
|-> vfs_fstat
| |-> fget
| |-> read_lock(&files->file_lock)
| |-> vfs_getattr
| |-> inode->i_op->getattr
| |-> generic_fillattr
|-> cp_new_stat64
|-> memset
|-> copy_to_user
so you're talking about contention on files->file_lock, right? it's really
not the kernel's fault that your app is badly written. that lock's private
to process & children, so it's not like another application can hurt you.
> What MCS locks do is they reduce the number of times
> the cacheline has to be flung around the system in
> order to get work done: they "scale" much better with
> the number of processors: O(N) instead of O(N^2).
yes, but how slow are they in the uncontended case?
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This archive was generated by hypermail 2b29 : Fri Nov 15 2002 - 22:00:16 EST