Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
MIME-Version: 1.0
References: <1607592918-14356-1-git-send-email-yejune.deng@gmail.com>
In-Reply-To: <1607592918-14356-1-git-send-email-yejune.deng@gmail.com>
From:   Eric Dumazet <edumazet@google.com>
Date:   Thu, 10 Dec 2020 11:19:36 +0100
Message-ID: <CANn89iKW4cLMssB2zi8kvikddVHMXfQLDr9Gkg768Ou3H5VwiA@mail.gmail.com>
Subject: Re: [PATCH] net: core: fix msleep() is not accurate
To:     Yejune Deng <yejune.deng@gmail.com>
Cc:     David Miller <davem@davemloft.net>,
        Jakub Kicinski <kuba@kernel.org>,
        Alexei Starovoitov <ast@kernel.org>,
        Andrii Nakryiko <andriin@fb.com>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Taehee Yoo <ap420073@gmail.com>,
        =?UTF-8?B?QmrDtnJuIFTDtnBlbA==?= <bjorn.topel@intel.com>,
        Cong Wang <xiyou.wangcong@gmail.com>,
        Jiri Pirko <jiri@mellanox.com>,
        netdev <netdev@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

On Thu, Dec 10, 2020 at 10:35 AM Yejune Deng <yejune.deng@gmail.com> wrote:
>
> See Documentation/timers/timers-howto.rst, msleep() is not
> for (1ms - 20ms), There is a more advanced API is used.
>
> Signed-off-by: Yejune Deng <yejune.deng@gmail.com>
> ---
>  net/core/dev.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/net/core/dev.c b/net/core/dev.c
> index d33099f..6e83ee03 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -6726,9 +6726,9 @@ void napi_disable(struct napi_struct *n)
>         set_bit(NAPI_STATE_DISABLE, &n->state);
>
>         while (test_and_set_bit(NAPI_STATE_SCHED, &n->state))
> -               msleep(1);
> +               fsleep(1000);
>         while (test_and_set_bit(NAPI_STATE_NPSVC, &n->state))
> -               msleep(1);
> +               fsleep(1000);
>

I would prefer explicit usleep_range().

fsleep() is not common in the kernel, I had to go to its definition.

I would argue that we should  use usleep_range(10, 200)  to have an
opportunity to spend less time in napi_disable() in some cases.