netdev.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Willem de Bruijn <willemdebruijn.kernel@gmail.com>
To: Cong Wang <xiyou.wangcong@gmail.com>
Cc: Alexander Duyck <alexander.duyck@gmail.com>,
	Eric Dumazet <edumazet@google.com>,
	sridhar.samudrala@intel.com,
	Linux Kernel Network Developers <netdev@vger.kernel.org>
Subject: Re: Three questions about busy poll
Date: Fri, 15 Feb 2019 17:46:23 -0500	[thread overview]
Message-ID: <CA+FuTSc-Oq0XWowxDEYeZ+oT6SG8YZSu5nvzeOO5sUq3v51Lvg@mail.gmail.com> (raw)
In-Reply-To: <CAM_iQpXYzPQ99foOzyN33xJDE7vdBWVg5ZNxrO6kuDAP1OLePQ@mail.gmail.com>

> > > 2. Why there is no socket option for sysctl.net.busy_poll? Clearly
> > > sysctl_net_busy_poll is global and SO_BUSY_POLL only works for
> > > sysctl.net.busy_read.
> >
> > I guess because of how sock_poll works. In that case it is not needed.
> > The poll duration applies more to the pollset than any of the
> > individual sockets, too.
>
>
> Good point, it's probably like struct eventpoll vs. struct epitem.
>
> The reason why I am looking for a per-socket tuning is to minimize
> the impact of setting busy_poll. I don't know if it is possible to somehow
> make this per-socket via epoll interfaces, perhaps fundamentally
> it is impossible?

I think it may be possible. The way busy_read and busy_poll work
in sock_poll is that the sum of all (per socket tunable) busy_read
durations on the sockets in the pollset is ~bound by (global) busy_poll.

The epoll implementation is restricted in the sense that it polls only
on one napi_id at a time. Alongside setting ep->napi_id in
ep_set_busy_poll_napi_id, we could also set a new ep field takes
the min of the global busy_poll and sk->sk_ll_usec.

Though I guess you want to be able to poll on a given pollset
without setting the global sysctl_net_busy_poll at all? That
would be a useful feature both for epoll and poll/select. But
definitely requires refining net_busy_loop_on() to optionally
take some state derived from the sockets in the (e)pollset.

  reply	other threads:[~2019-02-15 22:47 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-02-14 20:15 Cong Wang
2019-02-15  0:39 ` Willem de Bruijn
2019-02-15 19:04   ` Cong Wang
2019-02-15 22:46     ` Willem de Bruijn [this message]
2019-02-19  4:30       ` Cong Wang
2019-02-19 17:04         ` Willem de Bruijn
     [not found] ` <bfaff1c6-1269-1c33-31e1-0a78f78d7214@intel.com>
2019-02-15 19:18   ` Cong Wang
2019-02-22 20:00     ` Samudrala, Sridhar

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=CA+FuTSc-Oq0XWowxDEYeZ+oT6SG8YZSu5nvzeOO5sUq3v51Lvg@mail.gmail.com \
    --to=willemdebruijn.kernel@gmail.com \
    --cc=alexander.duyck@gmail.com \
    --cc=edumazet@google.com \
    --cc=netdev@vger.kernel.org \
    --cc=sridhar.samudrala@intel.com \
    --cc=xiyou.wangcong@gmail.com \
    --subject='Re: Three questions about busy poll' \
    /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

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).