linux-kernel - Re: [PATCH 04/11] sched,x86: Enable Turbo Boost Max Technology

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Message-ID: <20160824180854.GA1398@gmail.com>
Date:   Wed, 24 Aug 2016 20:08:54 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     Tim Chen <tim.c.chen@...ux.intel.com>
Cc:     Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        mingo@...hat.com, tglx@...utronix.de, hpa@...or.com,
        rjw@...ysocki.net, peterz@...radead.org, x86@...nel.org,
        bp@...e.de, sudeep.holla@....com, ak@...ux.intel.com,
        linux-acpi@...r.kernel.org, linux-pm@...r.kernel.org,
        alexey.klimov@....com, viresh.kumar@...aro.org,
        akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
        lenb@...nel.org, paul.gortmaker@...driver.com, jpoimboe@...hat.com,
        mcgrof@...nel.org, jgross@...e.com, robert.moore@...el.com,
        dvyukov@...gle.com, jeyu@...hat.com,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [PATCH 04/11] sched,x86: Enable Turbo Boost Max Technology


* Tim Chen <tim.c.chen@...ux.intel.com> wrote:

> Ingo,
> 
> This feature will be a clear benefit for client machines and
> less clear on servers.
> 
> This feature is most beneficial to single threaded workload running on
> a single socket that operates in mostly Turbo mode.  Client platform
> like Broadwell High End Desktop is the first one that supports it.
> Enablng this feature for such platform by default will be a win as it
> runs single threaded workload much of the time (10%-15% peformance
> upside).
> 
> On the other hand, a heavily loaded server that rarely operates in Turbo
> mode will benefit much less from this feature.  There is some overhead
> incurred by migrating load to the favored cores.  Some server folks
> have asked us to be cautious here and not to turn on ITMT scheduling
> by default.   Even so, when the server is lightly loaded, this feature
> can still be a win.  That said, this is future looking as we don't have
> any server with this feature today.
> 
> So if we take the approach to enable this feature by default for only
> single node system (using that as a criteria for client), will that seem
> reasonable to you?

I suppose that would work. Peter, any objections to such an approach?

Thanks,

	Ingo