From: Peter Zijlstra <peterz@infradead.org>
To: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: xinhui <xinhui.pan@linux.vnet.ibm.com>,
linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
virtualization@lists.linux-foundation.org, paulus@samba.org,
mpe@ellerman.id.au, mingo@redhat.com, paulmck@linux.vnet.ibm.com,
waiman.long@hpe.com
Subject: Re: [PATCH v5 1/6] qspinlock: powerpc support qspinlock
Date: Mon, 6 Jun 2016 17:59:07 +0200 [thread overview]
Message-ID: <20160606155907.GH30909@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <1464928427.26773.26.camel@kernel.crashing.org>
On Fri, Jun 03, 2016 at 02:33:47PM +1000, Benjamin Herrenschmidt wrote:
> - For the above, can you show (or describe) where the qspinlock
> improves things compared to our current locks.
So currently PPC has a fairly straight forward test-and-set spinlock
IIRC. You have this because LPAR/virt muck and lock holder preemption
issues etc..
qspinlock is 1) a fair lock (like ticket locks) and 2) provides
out-of-word spinning, reducing cacheline pressure.
Esp. on multi-socket x86 we saw the out-of-word spinning being a big win
over our ticket locks.
And fairness, brought to us by the ticket locks a long time ago,
eliminated starvation issues we had, where a spinner local to the holder
would 'always' win from a spinner further away. So under heavy enough
local contention, the spinners on 'remote' CPUs would 'never' get to own
the lock.
pv-qspinlock tries to preserve the fairness while allowing limited lock
stealing and explicitly managing which vcpus to wake.
> While there's
> theory and to some extent practice on x86, it would be nice to
> validate the effects on POWER.
Right; so that will have to be from benchmarks which I cannot help you
with ;-)
next prev parent reply other threads:[~2016-06-06 15:59 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <1464859370-5162-1-git-send-email-xinhui.pan@linux.vnet.ibm.com>
[not found] ` <1464859370-5162-3-git-send-email-xinhui.pan@linux.vnet.ibm.com>
[not found] ` <1464917520.26773.11.camel@kernel.crashing.org>
[not found] ` <1464917548.26773.12.camel@au1.ibm.com>
2016-06-03 4:10 ` [PATCH v5 1/6] qspinlock: powerpc support qspinlock xinhui
2016-06-03 4:33 ` Benjamin Herrenschmidt
2016-06-03 7:02 ` xinhui
2016-06-06 15:59 ` Peter Zijlstra [this message]
2016-06-06 21:41 ` Benjamin Herrenschmidt
2016-06-21 12:35 ` xinhui
2016-06-02 9:26 [PATCH v5 0/6] powerPC/pSeries use pv-qpsinlock as the default spinlock implemention Pan Xinhui
2016-06-02 9:26 ` [PATCH v5 1/6] qspinlock: powerpc support qspinlock Pan Xinhui
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