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SubjectRe: [Bugme-new] [Bug 15618] New: 2.6.18->2.6.32->2.6.33 huge regression in performance
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On Tue, 2010-03-23 at 20:14 +0100, Anton Starikov wrote:
> On Mar 23, 2010, at 6:45 PM, Linus Torvalds wrote:
>
> >
> >
> > On Tue, 23 Mar 2010, Ingo Molnar wrote:
> >>
> >> It shows a very brutal amount of page fault invoked mmap_sem spinning
> >> overhead.
> >
> > Isn't this already fixed? It's the same old "x86-64 rwsemaphores are using
> > the shit-for-brains generic version" thing, and it's fixed by
> >
> > 1838ef1 x86-64, rwsem: 64-bit xadd rwsem implementation
> > 5d0b723 x86: clean up rwsem type system
> > 59c33fa x86-32: clean up rwsem inline asm statements
> >
> > NOTE! None of those are in 2.6.33 - they were merged afterwards. But they
> > are in 2.6.34-rc1 (and obviously current -git). So Anton would have to
> > compile his own kernel to test his load.
>
>
> Applied mentioned patches. Things didn't improve too much.
>
> before:
> prog: Total exploration time 9.880 real 60.620 user 76.970 sys
>
> after:
> prog: Total exploration time 9.020 real 59.430 user 66.190 sys
>
> perf report:
>
> 38.58% prog [kernel] [k] _spin_lock_irqsave
> 37.42% prog ./prog [.] DBSLLlookup_ret
> 6.22% prog ./prog [.] SuperFastHash
> 3.65% prog /lib64/libc-2.11.1.so [.] __GI_memcpy
> 2.09% prog ./anderson.6.dve2C [.] get_successors
> 1.75% prog [kernel] [k] clear_page_c
> 1.73% prog ./prog [.] index_next_dfs
> 0.71% prog [kernel] [k] handle_mm_fault
> 0.38% prog ./prog [.] cb_hook
> 0.33% prog ./prog [.] get_local
> 0.32% prog [kernel] [k] page_fault

Could you verify with a callgraph profile what that spin_lock_irqsave()
is? If those rwsem patches were successfull mmap_sem should no longer
have a spinlock to content on, in which case it might be another lock.

If not, something went wrong with backporting those patches.


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