[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] RE: [Xen-devel] Re: hvm vpt lock strangeness
OK, thanks. So a per-vcpu list lock and a separate per-domain monotonicity lock are unfortunately both necessary (in my patch). > -----Original Message----- > From: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx > [mailto:xen-devel-bounces@xxxxxxxxxxxxxxxxxxx]On Behalf Of Keir Fraser > Sent: Friday, May 23, 2008 2:39 PM > To: dan.magenheimer@xxxxxxxxxx; Xen-Devel (E-mail) > Cc: Dave Winchell > Subject: [Xen-devel] Re: hvm vpt lock strangeness > > > Locking is required to prevent multiple concurrent access to a single > periodic timer. This is actually implemented at vcpu > granularity to avoid > lock juggling in functions which walk lists of timers. Since > those lists are > held per-vcpu, the convenient locking scope is the vcpu. > > -- Keir > > On 23/5/08 21:27, "Dan Magenheimer" > <dan.magenheimer@xxxxxxxxxx> wrote: > > > Noticed this a few days ago while working on the hvm-guest-time > > on xen-system-time patch, but forgot about it... > > > > Throughout xen/arch/x86/hvm/vpt.c, there are uses of a spinlock > > called tm_lock. But it appears that this spinlock is declared > > and used as part of a per-vcpu data structure. So is this > > somehow protecting against vcpu re-entrancy (didn't think that > > could happen) or is it supposed to be locking out one vcpu > > against another (and not doing the job because each vcpu has > > a separate lock)? Or am I misunderstanding something entirely? > > > > If this should be a domain-wide lock, I'll spin a patch. > > (And it might explain some of the weirder time problems?) > > > > Thanks, > > Dan > > > > =================================== > > Thanks... for the memory > > I really could use more / My throughput's on the floor > > The balloon is flat / My swap disk's fat / I've OOM's in store > > Overcommitted so much > > (with apologies to the late great Bob Hope) > > > > _______________________________________________ > Xen-devel mailing list > Xen-devel@xxxxxxxxxxxxxxxxxxx > http://lists.xensource.com/xen-devel > _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxx http://lists.xensource.com/xen-devel
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