On Wed, 17 Jan 2018, David Miller wrote: > From: Eric Dumazet <[email protected]> > Date: Wed, 17 Jan 2018 14:02:43 -0800 > > > On Wed, Jan 17, 2018 at 2:00 PM, Thomas Gleixner <[email protected]> wrote: > >> On Wed, 17 Jan 2018, Linus Torvalds wrote: > >> > >>> On Wed, Jan 17, 2018 at 1:54 PM, Thomas Gleixner <[email protected]> > >>> wrote: > >>> > raise_softirq() -> raise_softirq_irqoff() > >>> > > >>> > set_softirq_bit(); > >>> > > >>> > if (!in_interrupt()) > >>> > wake_softirqd(); > >>> > > >>> > So if the caller is not in hard or soft interrupt context, which > >>> > includes > >>> > bottom half disabled regions softirqd is woken. > >>> > >>> That does seem unnecessarily expensive, and maybe we could just do it > >>> with thread flag (TIF_NOTIFY_RESUME or whatever). > >>> > >>> In fact, that was what I *thought* we did. Maybe I just remember some > >>> historical behavior. > >>> > >>> Since networking seems to largely prefer softirqd anyway, maybe that > >>> wake_softirqd() is the right thing to do anyway. > >> > >> Well, but we only do it when we are not in a bh disabled region. The places > >> where thread context raises the network softirqs is usually inside a bh > >> disabled region, so the softirq is executed on local_bh_enable(). The > >> thread is woken up rarely. > > > > There is also the netif_rx_ni() stuff. > > > > Can't remember right now why it is not using > > local_bh_{diable,enable}() pair instead > > of preempt_disable() ... if (local_softirq_pending()) do_softirq(); > > Hmmm, that code predates the initial GIT repository build. > > I do remember we had some back and forth with that stuff.
commit 3ace873f40916682583562c1e1f324a4a50a2811 in https://git.kernel.org/pub/scm/linux/kernel/git/tglx/history.git deinlines that function and drops a comment while at it: -/* Post buffer to the network code from _non interrupt_ context. - * see net/core/dev.c for netif_rx description. - */ -static inline int netif_rx_ni(struct sk_buff *skb) It was added somewhere around 2.5.0 Thanks, tglx
