From: Ingo Molnar <mingo@kernel.org>
To: Jason Wang <jasowang@redhat.com>
Cc: Mike Galbraith <umgwanakikbuti@gmail.com>,
davem@davemloft.net, netdev@vger.kernel.org,
linux-kernel@vger.kernel.org, mst@redhat.com,
Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@elte.hu>
Subject: Re: [PATCH net-next 2/2] net: exit busy loop when another process is runnable
Date: Fri, 22 Aug 2014 09:42:24 +0200 [thread overview]
Message-ID: <20140822074224.GB7372@gmail.com> (raw)
In-Reply-To: <53F6F14B.1030609@redhat.com>
* Jason Wang <jasowang@redhat.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
next prev parent reply other threads:[~2014-08-22 7:42 UTC|newest]
Thread overview: 53+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-08-21 8:05 [PATCH net-next 1/2] sched: introduce nr_running_this_cpu() Jason Wang
2014-08-21 8:05 ` [PATCH net-next 2/2] net: exit busy loop when another process is runnable Jason Wang
2014-08-21 8:11 ` Michael S. Tsirkin
2014-08-22 2:53 ` Jason Wang
2014-08-21 19:03 ` Amos Kong
2014-08-22 5:01 ` Mike Galbraith
2014-08-22 7:29 ` Jason Wang
2014-08-22 7:42 ` Ingo Molnar [this message]
2014-08-29 3:08 ` Jason Wang
2014-09-01 6:39 ` Eliezer Tamir
2014-09-02 3:29 ` Jason Wang
2014-09-02 6:15 ` Eliezer Tamir
2014-09-02 7:37 ` Jason Wang
2014-09-02 8:31 ` Michael S. Tsirkin
2014-09-03 6:49 ` Eliezer Tamir
2014-09-03 7:33 ` Jason Wang
2014-09-03 9:36 ` Peter Zijlstra
2014-09-03 9:59 ` Michael S. Tsirkin
2014-09-03 7:51 ` Michael S. Tsirkin
2014-09-04 6:51 ` Eliezer Tamir
2014-08-22 7:36 ` Ingo Molnar
2014-08-22 9:08 ` Jason Wang
2014-08-22 14:16 ` Eric Dumazet
2014-08-25 2:54 ` Jason Wang
2014-08-25 13:16 ` Eliezer Tamir
2014-08-26 7:16 ` Jason Wang
2014-09-01 6:55 ` Eliezer Tamir
2014-09-02 3:35 ` Jason Wang
2014-09-02 6:03 ` Eliezer Tamir
2014-09-02 6:31 ` Jason Wang
2014-09-03 6:21 ` Eliezer Tamir
2014-09-03 6:59 ` Jason Wang
2016-04-14 0:55 ` Peter Zijlstra
2014-09-03 8:09 ` Michael S. Tsirkin
2016-04-11 16:31 ` Michael S. Tsirkin
2016-04-13 7:20 ` Ingo Molnar
2016-04-13 13:28 ` Peter Zijlstra
2016-04-13 13:51 ` Michael S. Tsirkin
2016-04-14 0:58 ` Peter Zijlstra
2014-09-01 9:31 ` Peter Zijlstra
2014-09-01 9:52 ` Michael S. Tsirkin
2014-09-01 10:04 ` Peter Zijlstra
2014-09-01 10:19 ` Peter Zijlstra
2014-09-02 4:03 ` Jason Wang
2014-09-02 10:24 ` Peter Zijlstra
2014-09-03 6:58 ` Jason Wang
2014-09-03 9:30 ` Peter Zijlstra
2014-09-01 10:22 ` Michael S. Tsirkin
2014-09-02 3:38 ` Jason Wang
2014-09-02 6:12 ` Peter Zijlstra
2014-09-02 7:19 ` Jason Wang
2014-08-21 13:52 ` [PATCH net-next 1/2] sched: introduce nr_running_this_cpu() Ingo Molnar
2014-08-22 7:27 ` Jason Wang
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