[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [Xen-devel] Re: [PATCH 00/14] PV ticket locks without expanding spinlock
On 11/16/2010 11:08 PM, Jeremy Fitzhardinge wrote: From: Jeremy Fitzhardinge<jeremy.fitzhardinge@xxxxxxxxxx> Hi all, This is a revised version of the pvticket lock series. The early part of the series is mostly unchanged: it converts the bulk of the ticket lock code into C and makes the "small" and "large" ticket code common. The only changes are the incorporation of various review comments. The latter part of the series converts from pv spinlocks to pv ticket locks (ie, using the ticket lock fastpath as-is, but adding pv ops for the ticketlock slowpaths). The significant difference here is that rather than adding a new ticket_t-sized element to arch_spinlock_t - effectively doubling the size - I steal the LSB of the tickets themselves to store a bit. This allows the structure to remain the same size, but at the cost of halving the max number of CPUs (127 for a 8-bit ticket, and a hard max of 32767 overall). The extra bit (well, two, but one is unused) in indicates whether the lock has gone into "slowpath state", which means one of its lockers has entered its slowpath and has blocked in the hypervisor. This means the current lock-holder needs to make sure it gets kicked out of the hypervisor on unlock. The spinlock remains in slowpath state until the last unlock happens (ie there are no more queued lockers). This code survives for a while with moderate testing, (make -j 100 on 8 VCPUs on a 4 PCPU system), but locks up after about 20 iterations, so there's still some race/deadlock in there (probably something misordered), but I think the basic approach is sound. This is going to be very useful for kvm; I'd like to see the fixed version gets merged. -- error compiling committee.c: too many arguments to function _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxx http://lists.xensource.com/xen-devel
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