On 2021/3/17 6:48, Cong Wang wrote:
On Mon, Mar 15, 2021 at 2:07 PM Jakub Kicinski kuba@kernel.org 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.
.