From: Peter Zijlstra <peterz@infradead.org>
To: Pan Xinhui <xinhui@linux.vnet.ibm.com>
Cc: linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org,
Benjamin Herrenschmidt <benh@kernel.crashing.org>,
Paul Mackerras <paulus@samba.org>,
Michael Ellerman <mpe@ellerman.id.au>,
Boqun Feng <boqun.feng@gmail.com>,
Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCH] powerpc: introduce {cmp}xchg for u8 and u16
Date: Tue, 12 Apr 2016 16:30:23 +0200 [thread overview]
Message-ID: <20160412143023.GH1087@worktop> (raw)
In-Reply-To: <570A6078.2050002@linux.vnet.ibm.com>
On Sun, Apr 10, 2016 at 10:17:28PM +0800, Pan Xinhui wrote:
>
> On 2016年04月08日 15:47, Peter Zijlstra wrote:
> > On Fri, Apr 08, 2016 at 02:41:46PM +0800, Pan Xinhui wrote:
> >> From: pan xinhui <xinhui.pan@linux.vnet.ibm.com>
> >>
> >> Implement xchg{u8,u16}{local,relaxed}, and
> >> cmpxchg{u8,u16}{,local,acquire,relaxed}.
> >>
> >> Atomic operation on 8-bit and 16-bit data type is supported from power7
> >
> > And yes I see nothing P7 specific here, this implementation is for
> > everything PPC64 afaict, no?
> >
> Hello Peter,
> No, it's not for every ppc. So yes, I need add #ifdef here. Thanks for pointing it out.
> We might need a new config option and let it depend on POWER7/POWER8_CPU or even POWER9...
Right, I'm not sure if PPC has alternatives, but you could of course
runtime patch the code from emulated with 32bit ll/sc to native 8/16bit
ll/sc if present on the current CPU if you have infrastructure for these
things.
> > Also, note that you don't need explicit 8/16 bit atomics to implement
> > these. Its fine to use 32bit atomics and only modify half the word.
> >
> That is true. But I am a little worried about the performance. It will
> forbid any other tasks to touch the other half word during the
> load/reserve, right?
Well, not forbid, it would just make the LL/SC fail and try again. Other
archs already implement them this way. See commit 3226aad81aa6 ("sh:
support 1 and 2 byte xchg") for example.
> I am working on the qspinlock implementation on PPC.
> Your and Waiman's patches are so nice. :)
Thanks!, last time I looked at PPC spinlocks they could not use things
like ticket locks because PPC might be a guest and fairness blows etc..
You're making the qspinlock-paravirt thing work on PPC, or doing
qspinlock only for bare-metal PPC?
next prev parent reply other threads:[~2016-04-12 14:30 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-04-08 6:41 [PATCH] powerpc: introduce {cmp}xchg for u8 and u16 Pan Xinhui
2016-04-08 7:47 ` Peter Zijlstra
2016-04-10 14:17 ` Pan Xinhui
2016-04-12 14:30 ` Peter Zijlstra [this message]
2016-04-13 11:15 ` Pan Xinhui
2016-04-13 15:53 ` Waiman Long
2016-04-14 8:31 ` Pan Xinhui
2016-04-16 19:43 ` Arnd Bergmann
2016-04-18 10:19 ` Pan Xinhui
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