Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
MIME-Version: 1.0
References: <20230325152417.5403-1-kerneljasonxing@gmail.com>
 <CANn89iJaVrObJNDC9TrnSUC3XQeo-zfmUXLVrNVcsbRDPuSNtA@mail.gmail.com>
 <CAL+tcoDVCywXXt0Whnx+o0PcULmdms0osJf0qUb0HKvVwuE6oQ@mail.gmail.com>
 <CAL+tcoCeyqMif1SDUq4MwfV0bBasgQ4LeYuQjPJYDKYLyof=Rw@mail.gmail.com> <CAL+tcoCFPKpDF+JBN1f74BxDJj9q=9ppoPntnCoT0gT6C0r=PA@mail.gmail.com>
In-Reply-To: <CAL+tcoCFPKpDF+JBN1f74BxDJj9q=9ppoPntnCoT0gT6C0r=PA@mail.gmail.com>
From:   Eric Dumazet <edumazet@google.com>
Date:   Sun, 26 Mar 2023 10:35:13 -0700
Message-ID: <CANn89iJLdce57j6fPbLpexp=tzTtw9yDwV7wjT5FbNF6fPkk+g@mail.gmail.com>
Subject: Re: [PATCH net] net: fix raising a softirq on the current cpu with
 rps enabled
To:     Jason Xing <kerneljasonxing@gmail.com>
Cc:     davem@davemloft.net, kuba@kernel.org, pabeni@redhat.com,
        netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
        Jason Xing <kernelxing@tencent.com>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

>
> Forgive me. Really I need some coffee. I made a mistake. This line
> above should be:
>
> +               if (!test_bit(NAPI_STATE_SCHED, &mysd->backlog.state))
>
> But the whole thing doesn't feel right. I need a few days to dig into
> this part until Eric can help me with more of it.
>

I am still traveling, and this is weekend time :/

It should not be too hard to read net/core/dev.c and remember that not
_all_ drivers (or some core networking functions) use the NAPI model.

eg look at netif_rx() and ask yourself why your patch is buggy.

Just look at callers of enqueue_to_backlog() and ask yourself if all
of them are called from net_rx_action()

[The answer is no, just in case you wonder]

In order to add your optimization, more work is needed, like adding
new parameters so that we do not miss critical
__raise_softirq_irqoff(NET_RX_SOFTIRQ) when _needed_.

We keep going circles around softirq deficiencies, I feel you are
trying to fix a second-order 'issue'.

Real cause is elsewhere, look at recent patches from Jakub.

Thanks.