Messages in this thread | | | Date | Thu, 11 Jun 2015 15:41:24 +0200 | From | Ingo Molnar <> | Subject | Re: [PATCH] x86/mm/fault: Put pgd_lock in its own cacheline |
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* Waiman Long <Waiman.Long@hp.com> wrote:
> On a large system with many cores, massive creation or destruction > of processes/threads can sometime cause a fair amount of spinlock > contention in the pgd_lock used by the pgd_alloc() and pgd_free() > functions. This patch tries to reduce false cacheline sharing by > putting the pgd_lock in its own cacheline which help to reduce > contention on the lock. > > Signed-off-by: Waiman Long <Waiman.Long@hp.com> > --- > arch/x86/mm/fault.c | 2 +- > 1 files changed, 1 insertions(+), 1 deletions(-) > > diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c > index 181c53b..fae48df 100644 > --- a/arch/x86/mm/fault.c > +++ b/arch/x86/mm/fault.c > @@ -185,7 +185,7 @@ force_sig_info_fault(int si_signo, int si_code, unsigned long address, > force_sig_info(si_signo, &info, tsk); > } > > -DEFINE_SPINLOCK(pgd_lock); > +__cacheline_aligned_in_smp DEFINE_SPINLOCK(pgd_lock); > LIST_HEAD(pgd_list);
Yeah, so if you are seeing pgd_lock contention we could do a lot more to improve the performance of pgd allocation than just putting it on a separate cacheline: we can actually eliminate pgd_list and turn all pgd_list users into RCU walkers of the tasklist lock, and make pgd_alloc()/pgd_free() lockless on x86.
I've done a series that implements this, I'll post it soon, please stay tuned!
Thanks,
Ingo
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