From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: Scott Wood <scottwood@freescale.com>
Cc: Tom Musta <tommusta@gmail.com>,
Peter Zijlstra <peterz@infradead.org>,
Raghavendra KT <raghavendra.kt.linux@gmail.com>,
Raghavendra KT <raghavendra.kt@linux.vnet.ibm.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Torsten Duwe <duwe@lst.de>, Anton Blanchard <anton@samba.org>,
Paul Mackerras <paulus@samba.org>,
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
linuxppc-dev@lists.ozlabs.org, Ingo Molnar <mingo@kernel.org>
Subject: Re: [PATCH v2] powerpc ticket locks
Date: Wed, 12 Feb 2014 06:34:28 +1100 [thread overview]
Message-ID: <1392147268.3835.11.camel@pasglop> (raw)
In-Reply-To: <1392143455.6733.386.camel@snotra.buserror.net>
On Tue, 2014-02-11 at 12:30 -0600, Scott Wood wrote:
> > It's something very special to IBM pSeries: the hypervisor can assign
> > fractions of physical CPUs to guests. Sometimes a guest with 4 quarter
> > CPUs will be faster than 1 monoprocessor. (correct me if I'm wrong).
> >
> > The directed yield resolves the silly situation when holder and waiter
> > reside on the same physical CPU, as I understand it.
> >
> > x86 has nothing comparable.
>
> How is this different from the very ordinary case of an SMP KVM guest
> whose vcpus are not bound to host cpus, and thus you could have multiple
> vcpus running on the same host cpu?
It's not really ... though I can see drawbacks with the scheme as well
and I think in KVM we should be careful to only confer if the owner
vcpu last scheduled on the same physical cpu where the waiter is, other
wise, there's too much chances of us bouncing things around the machine
for minor contention cases.
Paul, what's your policy today ?
Cheers,
Ben.
next prev parent reply other threads:[~2014-02-11 20:36 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-02-07 16:58 [PATCH v2] powerpc ticket locks Torsten Duwe
2014-02-07 17:12 ` Peter Zijlstra
2014-02-07 17:55 ` Torsten Duwe
2014-02-10 3:10 ` Benjamin Herrenschmidt
2014-02-10 15:52 ` Torsten Duwe
2014-02-10 17:53 ` Peter Zijlstra
2014-02-11 2:44 ` Benjamin Herrenschmidt
2014-02-11 2:56 ` Al Viro
2014-02-11 3:38 ` Benjamin Herrenschmidt
2014-02-11 9:53 ` Raghavendra KT
2014-02-11 10:40 ` Torsten Duwe
2014-02-11 18:30 ` Scott Wood
2014-02-11 19:34 ` Benjamin Herrenschmidt [this message]
2014-02-11 9:39 ` Raghavendra KT
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