On 10/13/2015 02:23 PM, Peter Zijlstra wrote:
On Tue, Sep 22, 2015 at 04:50:43PM -0400, Waiman Long wrote:for (;; waitcnt++) { + loop = SPIN_THRESHOLD; + while (loop) { + /* + * Spin until the lock is free + */ + for (; loop&& READ_ONCE(l->locked); loop--) + cpu_relax(); + /* + * Seeing the lock is free, this queue head vCPU is + * the rightful next owner of the lock. However, the + * lock may have just been stolen by another task which + * has entered the slowpath. So we need to use atomic + * operation to make sure that we really get the lock. + * Otherwise, we have to wait again. + */ + if (cmpxchg(&l->locked, 0, _Q_LOCKED_VAL) == 0) + goto gotlock; }for (loop = SPIN_THRESHOLD; loop; --loop) { if (!READ_ONCE(l->locked)&& cmpxchg(&l->locked, 0, _Q_LOCKED_VA) == 0) goto gotlock;cpu_relax(); }
This was the code that I used in my original patch, but it seems to confuse you about doing too many lock stealing. So I separated it out to make my intention more explicit. I will change it back to the old code.
Cheers, Longman -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
