On Fri, Aug 30, 2013 at 12:16 AM, Ingo Molnar <mingo@xxxxxxxxxx> wrote:
>
> * Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
>
>> > BTW. Do you have your test case at hand ?
>>
>> My test-case is a joke. It's explicitly *trying* to get as much
>> contention as possible on a dentry, by just starting up a lot of threads
>> that look up one single pathname (the same one for everybody). It
>> defaults to using /tmp for this, but you can specify the filename.
>
> Waiman's tests seemed to use sufficiently generic and varied workloads
> (AIM7) and they showed pretty nice unconditional improvements with his
> variant of this scheme, so I think testing with your simple testcase that
> intentionally magnifies the scalability issue is 100% legit and may in
> fact help tune the changes more accurately, because it has less inherent
> noise.
Yes. However, what I am (not very) worried about is that people will
hit some particular codepath that ends up having bad behavior.
I think I covered all the normal hotpaths in pathname lookup, which is
why I'm not *that* worried, but it's still the case that my silly
test-case is very limited. It's limited for a good *reason* (to try to
show the worst-case scalability problem), but it's limited.
Linus
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