On Thu, 2017-02-16 at 14:44 +0200, Saeed Mahameed wrote: > On Wed, Feb 15, 2017 at 4:04 PM, Eric Dumazet <eric.duma...@gmail.com> wrote: > > On Wed, 2017-02-15 at 05:29 -0800, Eric Dumazet wrote: > > > >> > >> mlx4_eq_int() is a hard irq handler. > >> > >> How a tasklet could run in the middle of it ? > >> > >> A tasklet is a softirq handler. > > > > Speaking of mlx4_eq_int() , 50% of cycles are spent on mb() (mfence) > > in eq_set_ci() > > > > I wonder why you have so many interrupts ? don't you have some kind of > interrupt moderation ? > what test are you running that got your CPU so busy.
Simply 8 RX queues. About 140,000 irq per second per RX queue, for a moderate network load on 40Gbit NIC. Interrupt moderation is a latency killer, we want our usec back. > > > I wonder why this very expensive mb() is required, right before exiting > > the interrupt handler. > > to make sure the HW knows we handled Completions up to (ci) consumer > index. so it will generate next irq. So why a mb() is needed exactly ? wmb() seems enough.
