linux-kernel - Re: [RFC PATCH 3/4] sched/topology: remove smt

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Message-Id: <20180905085029.GA57420@linux.vnet.ibm.com>
Date:   Wed, 5 Sep 2018 01:50:29 -0700
From:   Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
To:     Vincent Guittot <vincent.guittot@...aro.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH 3/4] sched/topology: remove smt_gain

* Vincent Guittot <vincent.guittot@...aro.org> [2018-09-05 09:36:42]:

> >
> > I dont know of any systems that have come with single threaded and
> > multithreaded. However some user can still offline few threads in a core
> > while leaving other cores untouched. I dont really know why somebody
> > would want to do it.  For example, some customer was toying with SMT 3
> > mode in a SMT 8 power8 box.
> 
> In this case, it means that we have the same core capacity whatever
> the number of CPUs
> and a core with SMT 3 will be set with the same compute capacity as
> the core with SMT 8.
> Does it still make sense ?
> 

To me it make sense atleast from  a power 8 perspective, because SMT 1 >
SMT 2 > SMT 4 > SMT8. So if one core is configured for SMT 2 and other
core is configured for SMT4; all threads being busy, the  individual
threads running on SMT2 core will complete more work than SMT 4 core
threads.

-- 
Thanks and Regards
Srikar Dronamraju