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Date: Thu, 09 Jul 2020 11:20:58 +0200 From: Paolo Abeni <pabeni@...hat.com> To: Cong Wang <xiyou.wangcong@...il.com> Cc: Josh Hunt <johunt@...mai.com>, Jonas Bonn <jonas.bonn@...rounds.com>, Michael Zhivich <mzhivich@...mai.com>, David Miller <davem@...emloft.net>, John Fastabend <john.fastabend@...il.com>, LKML <linux-kernel@...r.kernel.org>, Linux Kernel Network Developers <netdev@...r.kernel.org> Subject: Re: Packet gets stuck in NOLOCK pfifo_fast qdisc On Wed, 2020-07-08 at 13:16 -0700, Cong Wang wrote: > On Tue, Jul 7, 2020 at 7:18 AM Paolo Abeni <pabeni@...hat.com> wrote: > > So the regression with 2 pktgen threads is still relevant. 'perf' shows > > relevant time spent into net_tx_action() and __netif_schedule(). > > So, touching the __QDISC_STATE_SCHED bit in __dev_xmit_skb() is > not a good idea. > > Let me see if there is any other way to fix this. Thank you very much for the effort! I'm personally out of ideas for a real fix that would avoid regressions. To be more exaustive this are the sources of overhead, as far as I can observe them with perf: - contention on q->state, in __netif_schedule() - execution of net_tx_action() when there are no packet to be served Cheers, Paolo
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