From: Eric Dumazet <eric.dumazet@gmail.com>
To: Paolo Abeni <pabeni@redhat.com>, netdev@vger.kernel.org
Cc: "David S. Miller" <davem@davemloft.net>,
Willem de Bruijn <willemb@google.com>
Subject: Re: [RFC PATCH] net: don't keep lonely packets forever in the gro hash
Date: Tue, 20 Nov 2018 08:28:02 -0800 [thread overview]
Message-ID: <9773e2e6-a9b8-4663-932a-726e30b53b6c@gmail.com> (raw)
In-Reply-To: <e4a4bcfaa9f780a0b74ae453bfefd2768d9c8b5f.camel@redhat.com>
On 11/20/2018 07:42 AM, Paolo Abeni wrote:
> Hi,
>
> On Tue, 2018-11-20 at 05:49 -0800, Eric Dumazet wrote:
>>
>> On 11/20/2018 02:17 AM, Paolo Abeni wrote:
>>> Eric noted that with UDP GRO and napi timeout, we could keep a single
>>> UDP packet inside the GRO hash forever, if the related NAPI instance
>>> calls napi_gro_complete() at an higher frequency than the napi timeout.
>>> Willem noted that even TCP packets could be trapped there, till the
>>> next retransmission.
>>> This patch tries to address the issue, flushing the oldest packets before
>>> scheduling the NAPI timeout. The rationale is that such a timeout should be
>>> well below a jiffy and we are not flushing packets eligible for sane GRO.
>>>
>>> Reported-by: Eric Dumazet <eric.dumazet@gmail.com>
>>> Signed-off-by: Paolo Abeni <pabeni@redhat.com>
>>> ---
>>> Sending as RFC, as I fear I'm missing some relevant pieces.
>>> Also I'm unsure if this should considered a fixes for "udp: implement
>>> GRO for plain UDP sockets." or for "net: gro: add a per device gro flush timer"
>
> Thank you for your feedback!
>
>> Truth be told, relying on jiffies change is a bit fragile for HZ=100 or HZ=250 kernels.
>
> Yes, we have higher bound there.
>
>> See recent TCP commit that got rid of tcp_tso_should_defer() dependency on HZ/jiffies
>>
>> https://git.kernel.org/pub/scm/linux/kernel/git/davem/net-next.git/commit/?id=a682850a114aef947da5d603f7fd2cfe7eabbd72
>
> I'm unsure I follow correctly. Are you suggesting to use ns precision
> for skb aging in GRO? If so, could that be a separate change? (looks
> more invasive)
I am not suggesting adding ns in your patch.
That can be done later if we care.
I simply warn that some distros have low HZ value and thus the fix wont prevent packet sitting 4 or 10 ms in the queue.
next prev parent reply other threads:[~2018-11-21 2:58 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-11-20 10:17 [RFC PATCH] net: don't keep lonely packets forever in the gro hash Paolo Abeni
2018-11-20 11:30 ` Sergei Shtylyov
2018-11-20 13:49 ` Eric Dumazet
2018-11-20 15:42 ` Paolo Abeni
2018-11-20 16:28 ` Eric Dumazet [this message]
2018-11-21 9:13 ` Daniel Borkmann
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