Messages in this thread | | | Date | Wed, 6 Jan 2010 09:22:12 +0900 | From | KAMEZAWA Hiroyuki <> | Subject | Re: [RFC][PATCH 6/8] mm: handle_speculative_fault() |
| |
On Tue, 5 Jan 2010 07:26:31 -0800 (PST) Linus Torvalds <torvalds@linux-foundation.org> wrote:
> > > On Tue, 5 Jan 2010, KAMEZAWA Hiroyuki wrote: > > # > > # Overhead Command Shared Object Symbol > > # ........ ............... ........................ ...... > > # > > 43.23% multi-fault-all [kernel] [k] smp_invalidate_interrupt > > 16.27% multi-fault-all [kernel] [k] flush_tlb_others_ipi > > 11.55% multi-fault-all [kernel] [k] _raw_spin_lock_irqsave <========(*) > > 6.23% multi-fault-all [kernel] [k] intel_pmu_enable_all > > 2.17% multi-fault-all [kernel] [k] _raw_spin_unlock_irqrestore > > Hmm.. The default rwsem implementation shouldn't have any spin-locks in > the fast-path. And your profile doesn't seem to have any scheduler > footprint, so I wonder what is going on. > > Oh. > > Lookie here: > > - arch/x86/Kconfig.cpu: > > config X86_XADD > def_bool y > depends on X86_32 && !M386 > > - arch/x86/Kconfig: > > config RWSEM_GENERIC_SPINLOCK > def_bool !X86_XADD > > config RWSEM_XCHGADD_ALGORITHM > def_bool X86_XADD > > it looks like X86_XADD only gets enabled on 32-bit builds. Which means > that x86-64 in turn seems to end up always using the slower "generic > spinlock" version. > > Are you sure this isn't the reason why your profiles are horrible? > I think this is the 1st reason but haven't rewrote rwsem itself and tested, sorry.
This is a profile in other test. == 2.6.33-rc2's score of the same test program is here.
75.42% multi-fault-all [kernel] [k] _raw_spin_lock_irqsav | --- _raw_spin_lock_irqsave | |--49.13%-- __down_read_trylock | down_read_trylock | do_page_fault | page_fault | 0x400950 | | | --100.00%-- (nil) | |--46.92%-- __up_read | up_read | | | |--99.99%-- do_page_fault | | page_fault | | 0x400950 | | (nil) | --0.01%-- [...] == yes, spinlock is from rwsem.
Why I tried "skipping rwsem" is because I like avoid locking rather than rewrite lock itself when I think of the influence of the patch....
Thanks, -Kame
| |