Messages in this thread | | | From | Jason Xing <> | Date | Sun, 26 Mar 2023 12:04:07 +0800 | Subject | Re: [PATCH net] net: fix raising a softirq on the current cpu with rps enabled |
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On Sat, Mar 25, 2023 at 11:57 PM Eric Dumazet <edumazet@google.com> wrote: > > On Sat, Mar 25, 2023 at 8:26 AM Jason Xing <kerneljasonxing@gmail.com> wrote: > > > > From: Jason Xing <kernelxing@tencent.com> > > > > Since we decide to put the skb into a backlog queue of another > > cpu, we should not raise the softirq for the current cpu. When > > to raise a softirq is based on whether we have more data left to > > process later. As to the current cpu, there is no indication of > > more data enqueued, so we do not need this action. After enqueuing > > to another cpu, net_rx_action() function will call ipi and then > > another cpu will raise the softirq as expected. > > > > Also, raising more softirqs which set the corresponding bit field > > can make the IRQ mechanism think we probably need to start ksoftirqd > > on the current cpu. Actually it shouldn't happen. > > > > Fixes: 0a9627f2649a ("rps: Receive Packet Steering") > > Signed-off-by: Jason Xing <kernelxing@tencent.com> > > --- > > net/core/dev.c | 2 -- > > 1 file changed, 2 deletions(-) > > > > diff --git a/net/core/dev.c b/net/core/dev.c > > index 1518a366783b..bfaaa652f50c 100644 > > --- a/net/core/dev.c > > +++ b/net/core/dev.c > > @@ -4594,8 +4594,6 @@ static int napi_schedule_rps(struct softnet_data *sd) > > if (sd != mysd) { > > sd->rps_ipi_next = mysd->rps_ipi_list; > > mysd->rps_ipi_list = sd; > > - > > - __raise_softirq_irqoff(NET_RX_SOFTIRQ); > > return 1; > > } > > #endif /* CONFIG_RPS */ > > -- > > 2.37.3 > > > > This is not going to work in some cases. Please take a deeper look. > > I have to run, if you (or others) do not find the reason, I will give > more details when I am done traveling.
I'm wondering whether we could use @mysd instead of @sd like this:
if (!__test_and_set_bit(NAPI_STATE_SCHED, &mysd->backlog.state)) __raise_softirq_irqoff(NET_RX_SOFTIRQ);
I traced back to some historical changes and saw some relations with this commit ("net: solve a NAPI race"): https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=39e6c8208d7b6fb9d2047850fb3327db567b564b
Thanks, Jason
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