On 12/23/2014 03:52 AM, Ingo Molnar wrote:
to implement what Thomas suggested in the discussion: a proper
futex like spin mechanism? That looks like a totally acceptable
solution to me, without the disadvantages of your proposed
solution.
Hi Ingo,
Thank you for taking the time to respond. It is indeed possible to implement a futex like spin mechanism. Futex like mechanism will be clean and elegant. That is where I had started when I was given this problem to solve. Trouble I run into is the primary application I am looking at to help with this solution is Database which implements its own locking mechanism without using POSIX semaphore or futex. Since the locking is entirely in userspace, kernel has no clue when the userspace has acquired one of these locks. So I can see only two ways to solve this - find a solution in userspace entirely, or have userspace tell the kernel when it acquires one of these locks. I will spend more time on finding a way to solve it in userspace and see if I can find a way to leverage futex mechanism without causing significant change to database code. There may be a way to use priority inheritance to avoid contention. Database performance people tell me that their testing has shown the cost of making any system calls in this code easily offsets any gains from optimizing for contention avoidance, so that is one big challenge. Database rewriting their locking code is extremely unlikely scenario. Am I missing a third option here?
Thanks,
Khalid