linux-kernel - Re: [PATCH 2/2] x86/idle: use dynamic halt poll

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <4444ffc8-9e7b-5bd2-20da-af422fe834cc@redhat.com>
Date:   Thu, 22 Jun 2017 13:51:14 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     root <yang.zhang.wz@...il.com>, tglx@...utronix.de,
        mingo@...hat.com, hpa@...or.com
Cc:     x86@...nel.org, corbet@....net, tony.luck@...el.com, bp@...en8.de,
        peterz@...radead.org, mchehab@...nel.org,
        akpm@...ux-foundation.org, krzk@...nel.org, jpoimboe@...hat.com,
        luto@...nel.org, borntraeger@...ibm.com, thgarnie@...gle.com,
        rgerst@...il.com, minipli@...glemail.com,
        douly.fnst@...fujitsu.com, nicstange@...il.com, fweisbec@...il.com,
        dvlasenk@...hat.com, bristot@...hat.com,
        yamada.masahiro@...ionext.com, mika.westerberg@...ux.intel.com,
        yu.c.chen@...el.com, aaron.lu@...el.com, rostedt@...dmis.org,
        me@...ehuey.com, len.brown@...el.com, prarit@...hat.com,
        hidehiro.kawai.ez@...achi.com, fengtiantian@...wei.com,
        pmladek@...e.com, jeyu@...hat.com, Larry.Finger@...inger.net,
        zijun_hu@....com, luisbg@....samsung.com, johannes.berg@...el.com,
        niklas.soderlund+renesas@...natech.se, zlpnobody@...il.com,
        adobriyan@...il.com, fgao@...ai8.com, ebiederm@...ssion.com,
        subashab@...eaurora.org, arnd@...db.de, matt@...eblueprint.co.uk,
        mgorman@...hsingularity.net, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-edac@...r.kernel.org,
        kvm@...r.kernel.org
Subject: Re: [PATCH 2/2] x86/idle: use dynamic halt poll



On 22/06/2017 13:22, root wrote:
>  ==============================================================
>  
> +poll_grow: (X86 only)
> +
> +This parameter is multiplied in the grow_poll_ns() to increase the poll time.
> +By default, the values is 2.
> +
> +==============================================================
> +poll_shrink: (X86 only)
> +
> +This parameter is divided in the shrink_poll_ns() to reduce the poll time.
> +By default, the values is 2.

Even before starting the debate on whether this is a good idea or a bad
idea, KVM reduces the polling value to the minimum (10 us) by default
when polling fails.  Also, it shouldn't be bound to
CONFIG_HYPERVISOR_GUEST, since there's nothing specific to virtual
machines here.

Regarding the good/bad idea part, KVM's polling is made much more
acceptable by single_task_running().  At least you need to integrate it
with paravirtualization.  If the VM is scheduled out, you shrink the
polling period.  There is already vcpu_is_preempted for this, it is used
by mutexes.

Paolo