All of lore.kernel.org
 help / color / mirror / Atom feed
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

  reply	other threads:[~2014-08-22  7:42 UTC|newest]

Thread overview: 54+ 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
2014-09-04  8:25                         ` Michael S. Tsirkin
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

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20140822074224.GB7372@gmail.com \
    --to=mingo@kernel.org \
    --cc=davem@davemloft.net \
    --cc=jasowang@redhat.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=mingo@elte.hu \
    --cc=mst@redhat.com \
    --cc=netdev@vger.kernel.org \
    --cc=peterz@infradead.org \
    --cc=umgwanakikbuti@gmail.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body. 
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.