From: Marcelo Tosatti <mtosatti@redhat.com>
To: linux-kernel@vger.kernel.org, linux-rt-users@vger.kernel.org
Cc: Thomas Gleixner <tglx@linutronix.de>,
Anna-Maria Gleixner <anna-maria@linutronix.de>,
Daniel Bristot de Oliveira <bristot@redhat.com>,
Luiz Capitulino <lcapitulino@redhat.com>,
Haris Okanovic <haris.okanovic@ni.com>
Subject: Re: [patch 0/3] do not raise timer softirq unconditionally (spinlockless version)
Date: Mon, 6 May 2019 00:22:34 -0300 [thread overview]
Message-ID: <20190506032234.GA31395@amt.cnet> (raw)
In-Reply-To: <20190415201213.600254019@amt.cnet>
On Mon, Apr 15, 2019 at 05:12:13PM -0300, Marcelo Tosatti wrote:
> For isolated CPUs, we'd like to skip awakening ktimersoftd
> (the switch to and then back from ktimersoftd takes 10us in
> virtualized environments, in addition to other OS overhead,
> which exceeds telco requirements for packet forwarding for
> 5G) from the sched tick.
>
> The patch "timers: do not raise softirq unconditionally" from Thomas
> attempts to address that by checking, in the sched tick, whether its
> necessary to raise the timer softirq. Unfortunately, it attempts to grab
> the tvec base spinlock which generates the issue described in the patch
> "Revert "timers: do not raise softirq unconditionally"".
>
> tvec_base->lock protects addition of timers to the wheel versus
> timer interrupt execution.
>
> This patch does not grab the tvec base spinlock from irq context,
> but rather performs a lockless access to base->pending_map.
>
> It handles the the race between timer addition and timer interrupt
> execution by unconditionally (in case of isolated CPUs) raising the
> timer softirq after making sure the updated bitmap is visible
> on remote CPUs.
>
> This patchset reduces cyclictest latency from 25us to 14us
> on my testbox.
>
>
Ping?
next prev parent reply other threads:[~2019-05-06 3:23 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-04-15 20:12 [patch 0/3] do not raise timer softirq unconditionally (spinlockless version) Marcelo Tosatti
2019-04-15 20:12 ` [patch 1/3] timers: raise timer softirq on __mod_timer/add_timer_on Marcelo Tosatti
2019-05-29 14:53 ` Anna-Maria Gleixner
2019-05-30 19:23 ` Marcelo Tosatti
2019-04-15 20:12 ` [patch 2/3] timers: do not raise softirq unconditionally (spinlockless version) Marcelo Tosatti
2019-05-29 14:53 ` Anna-Maria Gleixner
2019-05-30 20:14 ` Marcelo Tosatti
2019-05-31 11:55 ` Anna-Maria Gleixner
2019-06-11 11:45 ` Anna-Maria Gleixner
2019-06-04 6:29 ` Peter Xu
2019-06-06 15:14 ` Marcelo Tosatti
2019-04-15 20:12 ` [patch 3/3] timers: condense pending bitmap information Marcelo Tosatti
2019-04-15 20:17 ` [patch 0/3] do not raise timer softirq unconditionally (spinlockless version) Marcelo Tosatti
2019-05-06 3:22 ` Marcelo Tosatti [this message]
2019-05-06 7:17 ` Daniel Bristot de Oliveira
2019-05-06 9:22 ` Thomas Gleixner
2019-05-29 14:52 ` Anna-Maria Gleixner
2019-05-30 19:38 ` Marcelo Tosatti
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=20190506032234.GA31395@amt.cnet \
--to=mtosatti@redhat.com \
--cc=anna-maria@linutronix.de \
--cc=bristot@redhat.com \
--cc=haris.okanovic@ni.com \
--cc=lcapitulino@redhat.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-rt-users@vger.kernel.org \
--cc=tglx@linutronix.de \
/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 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).