linux-kernel.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Paolo Bonzini <pbonzini@redhat.com>
To: "Radim Krčmář" <rkrcmar@redhat.com>
Cc: Wanpeng Li <kernellwp@gmail.com>,
	Yang Zhang <yang.zhang.wz@gmail.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
	the arch/x86 maintainers <x86@kernel.org>,
	Jonathan Corbet <corbet@lwn.net>,
	tony.luck@intel.com, Borislav Petkov <bp@alien8.de>,
	Peter Zijlstra <peterz@infradead.org>,
	mchehab@kernel.org, Andrew Morton <akpm@linux-foundation.org>,
	krzk@kernel.org, jpoimboe@redhat.com,
	Andy Lutomirski <luto@kernel.org>,
	Christian Borntraeger <borntraeger@de.ibm.com>,
	Thomas Garnier <thgarnie@google.com>,
	Robert Gerst <rgerst@gmail.com>,
	Mathias Krause <minipli@googlemail.com>,
	douly.fnst@cn.fujitsu.com, Nicolai Stange <nicstange@gmail.com>,
	Frederic Weisbecker <fweisbec@gmail.com>,
	dvlasenk@redhat.com,
	Daniel Bristot de Oliveira <bristot@redhat.com>,
	yamada.masahiro@socionext.com, mika.westerberg@linux.intel.com,
	Chen Yu <yu.c.chen@intel.com>,
	aaron.lu@intel.com, Steven Rostedt <rostedt@goodmis.org>,
	Kyle Huey <me@kylehuey.com>, Len Brown <len.brown@intel.com>,
	Prarit Bhargava <prarit@redhat.com>,
	hidehiro.kawai.ez@hitachi.com, fengtiantian@huawei.com,
	pmladek@suse.com, jeyu@redhat.com, Larry.Finger@lwfinger.net,
	zijun_hu@htc.com, luisbg@osg.samsung.com,
	johannes.berg@intel.com, niklas.soderlund+renesas@ragnatech.se,
	zlpnobody@gmail.com, Alexey Dobriyan <adobriyan@gmail.com>,
	fgao@48lvckh6395k16k5.yundunddos.com, ebiederm@xmission.com,
	Subash Abhinov Kasiviswanathan <subashab@codeaurora.org>,
	Arnd Bergmann <arnd@arndb.de>,
	Matt Fleming <matt@codeblueprint.co.uk>,
	Mel Gorman <mgorman@techsingularity.net>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	linux-doc@vger.kernel.org, linux-edac@vger.kernel.org,
	kvm <kvm@vger.kernel.org>
Subject: Re: [PATCH 2/2] x86/idle: use dynamic halt poll
Date: Tue, 27 Jun 2017 15:56:35 +0200	[thread overview]
Message-ID: <2771f905-d1b0-b118-9ae9-db5fb87f877c@redhat.com> (raw)
In-Reply-To: <20170627134043.GA1487@potion>



On 27/06/2017 15:40, Radim Krčmář wrote:
>> ... which is not necessarily _wrong_.  It's just a different heuristic.
> Right, it's just harder to use than host's single_task_running() -- the
> VCPU calling vcpu_is_preempted() is never preempted, so we have to look
> at other VCPUs that are not halted, but still preempted.
> 
> If we see some ratio of preempted VCPUs (> 0?), then we stop polling and
> yield to the host.  Working under the assumption that there is work for
> this PCPU if other VCPUs have stuff to do.  The downside is that it
> misses information about host's topology, so it would be hard to make it
> work well.

I would just use vcpu_is_preempted on the current CPU.  From guest POV
this option is really a "f*** everyone else" setting just like
idle=poll, only a little more polite.

If we've been preempted and we were polling, there are two cases.  If an
interrupt was queued while the guest was preempted, the poll will be
treated as successful anyway.  If it hasn't, let others run---but really
that's not because the guest wants to be polite, it's to avoid that the
scheduler penalizes it excessively.

So until it's preempted, I think it's okay if the guest doesn't care
about others.  You wouldn't use this option anyway in overcommitted
situations.

(I'm still not very convinced about the idea).

Paolo

  reply	other threads:[~2017-06-27 13:57 UTC|newest]

Thread overview: 37+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-06-22 11:22 [PATCH 0/2] x86/idle: add halt poll support root
2017-06-22 11:22 ` [PATCH 1/2] x86/idle: add halt poll for halt idle root
2017-06-22 14:23   ` Thomas Gleixner
2017-06-23  4:05     ` Yang Zhang
2017-08-16  4:04   ` Michael S. Tsirkin
2017-08-17  7:29     ` Yang Zhang
2017-06-22 11:22 ` [PATCH 2/2] x86/idle: use dynamic halt poll root
2017-06-22 11:51   ` Paolo Bonzini
2017-06-23  3:58     ` Yang Zhang
2017-06-27 11:22       ` Yang Zhang
2017-06-27 12:07         ` Paolo Bonzini
2017-06-27 12:23           ` Wanpeng Li
2017-06-27 12:28             ` Paolo Bonzini
2017-06-27 13:40               ` Radim Krčmář
2017-06-27 13:56                 ` Paolo Bonzini [this message]
2017-06-27 14:22                   ` Radim Krčmář
2017-06-27 14:26                     ` Paolo Bonzini
2017-07-03  9:28                     ` Yang Zhang
2017-07-03 10:06                       ` Thomas Gleixner
2017-07-04  2:19                         ` Yang Zhang
2017-07-04 14:13                       ` Radim Krčmář
2017-07-04 14:50                         ` Thomas Gleixner
2017-07-13 11:49                         ` Yang Zhang
2017-07-14  9:37                           ` Alexander Graf
2017-07-17  9:26                             ` Yang Zhang
2017-07-17  9:54                               ` Alexander Graf
2017-07-17 12:50                                 ` Yang Zhang
2017-07-04 22:28                       ` Wanpeng Li
2017-06-22 14:32   ` Thomas Gleixner
2017-06-23  4:04     ` Yang Zhang
2017-06-22 22:46   ` kbuild test robot
2017-06-22 11:32 ` [PATCH 0/2] x86/idle: add halt poll support Yang Zhang
2017-06-22 11:50 ` Wanpeng Li
2017-06-23  4:08   ` Yang Zhang
2017-06-23  4:35     ` Wanpeng Li
2017-06-23  6:49       ` Yang Zhang
2017-06-27 14:00         ` Radim Krčmář

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=2771f905-d1b0-b118-9ae9-db5fb87f877c@redhat.com \
    --to=pbonzini@redhat.com \
    --cc=Larry.Finger@lwfinger.net \
    --cc=aaron.lu@intel.com \
    --cc=adobriyan@gmail.com \
    --cc=akpm@linux-foundation.org \
    --cc=arnd@arndb.de \
    --cc=borntraeger@de.ibm.com \
    --cc=bp@alien8.de \
    --cc=bristot@redhat.com \
    --cc=corbet@lwn.net \
    --cc=douly.fnst@cn.fujitsu.com \
    --cc=dvlasenk@redhat.com \
    --cc=ebiederm@xmission.com \
    --cc=fengtiantian@huawei.com \
    --cc=fgao@48lvckh6395k16k5.yundunddos.com \
    --cc=fweisbec@gmail.com \
    --cc=hidehiro.kawai.ez@hitachi.com \
    --cc=hpa@zytor.com \
    --cc=jeyu@redhat.com \
    --cc=johannes.berg@intel.com \
    --cc=jpoimboe@redhat.com \
    --cc=kernellwp@gmail.com \
    --cc=krzk@kernel.org \
    --cc=kvm@vger.kernel.org \
    --cc=len.brown@intel.com \
    --cc=linux-doc@vger.kernel.org \
    --cc=linux-edac@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=luisbg@osg.samsung.com \
    --cc=luto@kernel.org \
    --cc=matt@codeblueprint.co.uk \
    --cc=mchehab@kernel.org \
    --cc=me@kylehuey.com \
    --cc=mgorman@techsingularity.net \
    --cc=mika.westerberg@linux.intel.com \
    --cc=mingo@redhat.com \
    --cc=minipli@googlemail.com \
    --cc=nicstange@gmail.com \
    --cc=niklas.soderlund+renesas@ragnatech.se \
    --cc=peterz@infradead.org \
    --cc=pmladek@suse.com \
    --cc=prarit@redhat.com \
    --cc=rgerst@gmail.com \
    --cc=rkrcmar@redhat.com \
    --cc=rostedt@goodmis.org \
    --cc=subashab@codeaurora.org \
    --cc=tglx@linutronix.de \
    --cc=thgarnie@google.com \
    --cc=tony.luck@intel.com \
    --cc=x86@kernel.org \
    --cc=yamada.masahiro@socionext.com \
    --cc=yang.zhang.wz@gmail.com \
    --cc=yu.c.chen@intel.com \
    --cc=zijun_hu@htc.com \
    --cc=zlpnobody@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 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).