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Message-ID: <20140822074224.GB7372@gmail.com> Date: Fri, 22 Aug 2014 09:42:24 +0200 From: Ingo Molnar <mingo@...nel.org> To: Jason Wang <jasowang@...hat.com> Cc: Mike Galbraith <umgwanakikbuti@...il.com>, davem@...emloft.net, netdev@...r.kernel.org, linux-kernel@...r.kernel.org, mst@...hat.com, Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...e.hu> Subject: Re: [PATCH net-next 2/2] net: exit busy loop when another process is runnable * Jason Wang <jasowang@...hat.com> wrote: > Polling could be done by either rx busy loop in process > context or NAPI in softirq. [...] Note that this shows another reason why it's a bad idea to query nr_running directly: depending on the softirq processing method, a softirq might run: - directly in process context - in an idle thread's context - or in a ksoftirqd context. 'nr_running' will have different values in these cases, causing assymetries in busy-poll handling! Another class of assymetry is when there are other softirq bits pending, beyond NET_RX (or NET_TX): a nr_running check misses them. The solution I outlined in the previous mail (using a sched_expected_runtime() method) would be able to avoid most of these artifacts. Thanks, Ingo -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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