On 2021/3/17 6:48, Cong Wang wrote: > On Mon, Mar 15, 2021 at 2:07 PM Jakub Kicinski <kuba@xxxxxxxxxx> wrote: >> >> I thought pfifo was supposed to be "lockless" and this change >> re-introduces a lock between producer and consumer, no? > > It has never been truly lockless, it uses two spinlocks in the ring buffer > implementation, and it introduced a q->seqlock recently, with this patch > now we have priv->lock, 4 locks in total. So our "lockless" qdisc ends > up having more locks than others. ;) I don't think we are going to a > right direction... Yes, we have 4 locks in total, but lockless qdisc only use two locks in this patch, which are priv->lock and q->seqlock. The qdisc at least uses two locks, which is qdisc_lock(q) and q->busylock, which seems to have bigger contention when concurrent accessing to the same qdisc. If we want to reduce the total number of lock, we can use qdisc_lock(q) for lockless qdisc and remove q->seqlock:) > > Thanks. > > . >
