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[Xen-devel] Re: [PATCH RFC 10/12] x86/pvticketlock: keep count of blocke

To: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Subject: [Xen-devel] Re: [PATCH RFC 10/12] x86/pvticketlock: keep count of blocked cpus
From: Nick Piggin <npiggin@xxxxxxx>
Date: Tue, 3 Aug 2010 19:44:51 +1000
Cc: Nick Piggin <npiggin@xxxxxxx>, Jeremy Fitzhardinge <jeremy@xxxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>, Linux Kernel Mailing List <linux-kernel@xxxxxxxxxxxxxxx>, Jan Beulich <JBeulich@xxxxxxxxxx>, Avi Kivity <avi@xxxxxxxxxx>
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References: <cover.1279328276.git.jeremy.fitzhardinge@xxxxxxxxxx> <9d5625e61c7f35e72156e8cb881e55910b4fa5dc.1279328276.git.jeremy.fitzhardinge@xxxxxxxxxx> <1280824360.1923.421.camel@laptop>
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On Tue, Aug 03, 2010 at 10:32:40AM +0200, Peter Zijlstra wrote:
> On Fri, 2010-07-16 at 18:03 -0700, Jeremy Fitzhardinge wrote:
> > @@ -26,6 +26,9 @@ typedef struct arch_spinlock {
> >                         __ticket_t head, tail;
> >                 } tickets;
> >         };
> > +       __ticket_t waiting;
> > +#endif
> >  } arch_spinlock_t; 
> This bloats spinlock_t from u32 to u64 on most distro configs I think,
> since they'll have NR_CPUS=4096 or something large like that and
> probably also want to have this PARAVIRT_SPINLOCKS thing.

Which sucks for carefully packed data structures like dentry.
They'll tend to grow by 8 bytes per spinlock.

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