From: Benjamin Herrenschmidt <benh@au1.ibm.com>
To: "'Naveen N. Rao'" <naveen.n.rao@linux.vnet.ibm.com>,
David Laight <David.Laight@ACULAB.COM>
Cc: "daniel@iogearbox.net" <daniel@iogearbox.net>,
"ast@fb.com" <ast@fb.com>,
"netdev@vger.kernel.org" <netdev@vger.kernel.org>,
"linuxppc-dev@lists.ozlabs.org" <linuxppc-dev@lists.ozlabs.org>,
"davem@davemloft.net" <davem@davemloft.net>
Subject: Re: [PATCH 3/3] powerpc: bpf: implement in-register swap for 64-bit endian operations
Date: Sun, 15 Jan 2017 09:00:58 -0600 [thread overview]
Message-ID: <1484492458.11927.17.camel@au1.ibm.com> (raw)
In-Reply-To: <20170113175201.GD3470@naverao1-tp.localdomain>
On Fri, 2017-01-13 at 23:22 +0530, 'Naveen N. Rao' wrote:
> > That rather depends on whether the processor has a store to load forwarder
> > that will satisfy the read from the store buffer.
> > I don't know about ppc, but at least some x86 will do that.
>
> Interesting - good to know that.
>
> However, I don't think powerpc does that and in-register swap is likely
> faster regardless. Note also that gcc prefers this form at higher
> optimization levels.
Of course powerpc has a load-store forwarder these days, however, I
wouldn't be surprised if the in-register form was still faster on some
implementations, but this needs to be tested.
Ideally, you'd want to try to "optimize" load+swap or swap+store
though.
Cheers,
Ben.
next prev parent reply other threads:[~2017-01-15 15:01 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-01-13 17:10 [PATCH 1/3] powerpc: bpf: remove redundant check for non-null image Naveen N. Rao
2017-01-13 17:10 ` [PATCH 2/3] powerpc: bpf: flush the entire JIT buffer Naveen N. Rao
2017-01-13 20:10 ` Alexei Starovoitov
2017-01-13 22:55 ` Daniel Borkmann
2017-01-27 0:40 ` [2/3] " Michael Ellerman
2017-01-13 17:10 ` [PATCH 3/3] powerpc: bpf: implement in-register swap for 64-bit endian operations Naveen N. Rao
2017-01-13 17:17 ` David Laight
2017-01-13 17:52 ` 'Naveen N. Rao'
2017-01-15 15:00 ` Benjamin Herrenschmidt [this message]
2017-01-23 19:22 ` 'Naveen N. Rao'
2017-01-24 16:13 ` David Laight
2017-01-24 16:25 ` 'Naveen N. Rao'
2017-01-13 20:09 ` [PATCH 1/3] powerpc: bpf: remove redundant check for non-null image Alexei Starovoitov
2017-01-16 18:38 ` David Miller
2017-01-23 17:14 ` Naveen N. Rao
2017-01-27 0:40 ` [1/3] " Michael Ellerman
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