linux-kernel - Re: [PATCH] net: core: fix msleep() is not accurate

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Date:   Thu, 10 Dec 2020 11:19:36 +0100
From:   Eric Dumazet <edumazet@...gle.com>
To:     Yejune Deng <yejune.deng@...il.com>
Cc:     David Miller <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Andrii Nakryiko <andriin@...com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Taehee Yoo <ap420073@...il.com>,
        Björn Töpel <bjorn.topel@...el.com>,
        Cong Wang <xiyou.wangcong@...il.com>,
        Jiri Pirko <jiri@...lanox.com>,
        netdev <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] net: core: fix msleep() is not accurate

On Thu, Dec 10, 2020 at 10:35 AM Yejune Deng <yejune.deng@...il.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@...il.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.