From: "David Laight" <David.Laight@ACULAB.COM>
To: "Segher Boessenkool" <segher@kernel.crashing.org>,
"Anton Blanchard" <anton@samba.org>
Cc: paulus@samba.org, Michael Neuling <mikey@neuling.org>,
sukadev@linux.vnet.ibm.com, linuxppc-dev@lists.ozlabs.org
Subject: RE: [PATCH] powerpc: POWER7 optimised copy_to_user/copy_from_user using VMX
Date: Thu, 8 Dec 2011 14:02:39 -0000 [thread overview]
Message-ID: <AE90C24D6B3A694183C094C60CF0A2F6D8AF0A@saturn3.aculab.com> (raw)
In-Reply-To: <700CAC5A-AD1A-48BA-BD74-CB9FBB325484@kernel.crashing.org>
=20
> > One idea would be to have a structure of function pointers for each
> > CPU that gets runtime patched into the right places,=20
> > similar to how we do some of the MMU fixups.
>=20
> Sounds good to me :-)
Except the indirect jump/call is almost certainly
never predicted - so will be slow.
You might want to patch jump instructions instead.
The same is true for in-kernel memcpy() and other
similar operations.
I actually wonder sometimes what the typical lengths
are for these sort of functions, and whether, in fact,
small lengths dominate - where the fixed costs matter.
David
next prev parent reply other threads:[~2011-12-08 14:02 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-12-08 5:02 [PATCH] powerpc: POWER7 optimised copy_to_user/copy_from_user using VMX Anton Blanchard
2011-12-08 5:44 ` Kumar Gala
2011-12-08 5:54 ` Michael Neuling
2011-12-08 6:04 ` Anton Blanchard
2011-12-08 13:31 ` Segher Boessenkool
2011-12-08 14:02 ` David Laight [this message]
2011-12-08 14:12 ` Segher Boessenkool
2011-12-08 19:40 ` Benjamin Herrenschmidt
2011-12-08 6:11 ` Anton Blanchard
2011-12-19 3:00 ` Benjamin Herrenschmidt
2011-12-19 3:19 ` Benjamin Herrenschmidt
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