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SubjectRe: [PATCH v2 0/4] ipc: reduce ipc lock contention
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On Tue, 2013-03-05 at 07:40 -0800, Linus Torvalds wrote:
> On Tue, Mar 5, 2013 at 1:35 AM, Davidlohr Bueso <davidlohr.bueso@hp.com> wrote:
> >
> > The following set of patches are based on the discussion of holding the
> > ipc lock unnecessarily, such as for permissions and security checks:
>
> Ok, looks fine from a quick look (but then, so did your previous patch-set ;)
>
> You still open-code the spinlock in at least a few places (I saw
> sem_getref), but I still don't care deeply.
>
> >> 2) While on an Oracle swingbench DSS (data mining) workload the
> > improvements are not as exciting as with Rik's benchmark, we can see
> > some positive numbers. For an 8 socket machine the following are the
> > percentages of %sys time incurred in the ipc lock:
>
> Ok, I hoped for it being more noticeable. Since that benchmark is less
> trivial than Rik's, can you do a perf record -fg of it and give a more
> complete picture of what the kernel footprint is - and in particular
> who now gets that ipc lock function? Is it purely semtimedop, or what?
> Look out for inlining - ipc_rcu_getref() looks like it would be
> inlined, for example.
>
> It would be good to get a "top twenty kernel functions" from the
> profile, along with some call data on where the lock callers are.. I
> know that Rik's benchmark *only* had that one call-site, I'm wondering
> if the swingbench one has slightly more complex behavior...

For a 400 user workload (the kernel functions remain basically the same
for any amount of users):

17.86% oracle [kernel.kallsyms] [k] _raw_spin_lock
8.46% swapper [kernel.kallsyms] [k] intel_idle
5.51% oracle [kernel.kallsyms] [k] try_atomic_semop
5.05% oracle [kernel.kallsyms] [k] update_sd_lb_stats
2.81% oracle [kernel.kallsyms] [k] tg_load_down
2.41% swapper [kernel.kallsyms] [k] update_blocked_averages
2.38% oracle [kernel.kallsyms] [k] idle_cpu
2.37% swapper [kernel.kallsyms] [k] native_write_msr_safe
2.28% oracle [kernel.kallsyms] [k] update_cfs_rq_blocked_load
1.84% oracle [kernel.kallsyms] [k] update_blocked_averages
1.79% oracle [kernel.kallsyms] [k] update_queue
1.73% swapper [kernel.kallsyms] [k] update_cfs_rq_blocked_load
1.29% oracle [kernel.kallsyms] [k] native_write_msr_safe
1.07% java [kernel.kallsyms] [k] update_sd_lb_stats
0.91% swapper [kernel.kallsyms] [k] poll_idle
0.86% oracle [kernel.kallsyms] [k] try_to_wake_up
0.80% java [kernel.kallsyms] [k] tg_load_down
0.72% oracle [kernel.kallsyms] [k] load_balance
0.67% oracle [kernel.kallsyms] [k] __schedule
0.67% oracle [kernel.kallsyms] [k] cpumask_next_and

Digging into the _raw_spin_lock call:

17.86% oracle [kernel.kallsyms] [k] _raw_spin_lock
|
--- _raw_spin_lock
|
|--49.55%-- sys_semtimedop
| |
| |--77.41%-- system_call
| | semtimedop
| | skgpwwait
| | ksliwat
| | kslwaitctx


Thanks,
Davidlohr




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