On 08/02/2010 05:42 PM, Ryan Harper wrote:
A problem with directed yield is figuring out who to yield to. One idea
is to look for a random vcpu that is not running and donate some runtime
to it. In the best case, it's the lock holder and we cause it to start
running. Middle case it's not the lock holder, but we lose enough
runtime to stop running, so at least we don't waste cpu. Worst case we
continue running not having woken the lock holder. Spin again, yield
again hoping to find the right vcpu.
It's been quite some time, but played with directed yielding for Xen[1]
and we were looking to model the POWER directed yield (H_CONFER) where
the lock holding vcpu was indiciated in the spinlock. When acquiring
the lock, record the vcpu id. When another vcpu attempts to acquire the
lock if it can't it can yield its time to the lock holder.
No reason why we can't have something similar.
We can take the lock and set the owner atomically:
LOCK_PREFIX "cmpxchg %1, %0"
: "=m"(lock) : "r"(raw_smp_processor_id() | SPIN_LOCK_BIAS),
"a"((u16)0) : "memory"
--
error compiling committee.c: too many arguments to function
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