From: Eric Van Hensbergen <ericvh@gmail.com>
To: Michael Neuling <mikey@neuling.org>
Cc: linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org,
bg-linux@lists.anl-external.org
Subject: Re: [PATCH 3/7] [RFC] add support for BlueGene/P FPU
Date: Thu, 19 May 2011 16:55:06 -0500 [thread overview]
Message-ID: <BANLkTi=rc5vZm3xAXHpHSxSH1wBWKhv92A@mail.gmail.com> (raw)
In-Reply-To: <29601.1305840992@neuling.org>
Damnit Mikey, just after I hit send on [V2].....
On Thu, May 19, 2011 at 4:36 PM, Michael Neuling <mikey@neuling.org> wrote:
> In message <BANLkTimKhApFW8G1-pG0u_9Kv2YB0R1O0w@mail.gmail.com> you wrote=
:
>> On Thu, May 19, 2011 at 12:58 AM, Michael Neuling <mikey@neuling.org> wr=
ote=3D
>> :
>> > Eric,
>> >
>> >> This patch adds save/restore register support for the BlueGene/P
>> >> double hummer FPU.
>> >
>> > What does this mean? =3DA0Needs more details here.
>> >
okay, I've changed it a bit in [V2], if you want more I can do my best.
>> "Each of the two FPU units contains 32 64-bit floating point registers
>> for a total of 64 FP registers per processor." which would seem to
>> point to the kittyhawk version - but they have a second SAVE_32SFPRS
>> for the second hummer. =A0What wasn't clear to me with this version of
>> the code was whether or not they were doing something clever like
>> saving the pair of the 64-bit FPU registers in a single 128-bit slot
>> (seems plausible).
>
> Ok, sounds like there is 32*8*2 bytes of data, rather than the normal
> 32*8 bytes for FP only (ignoring VSX). =A0If this is the case, then you'l=
l
> need make 'fpr' in the thread struct bigger which you can do by setting
> TS_FPRWIDTH =3D 2 like we do for VSX.
>
Okay, I'll incorporate that into [V3].
> If there is some instruction that saves and restores two of these at a
> time (which LFPDX/STFPDX might I guess), then we can use that, otherwise
> we'll have to do 64 saves/restores. =A0Double load/stores will be faster
> I'm guessing though.
I assume that's true.
>
> If two at a time, do we need to increase the index in pairs?
>
I don't believe so.
>> If this is not the way to go, I can certainly
>> switch the kittyhawk version of the patch with the *, the extra
>> SAVE32SFPR and the extra double hummer specific storage space in the
>> thread_struct.
>
> I'd be tempted to keep it in the 'fpr' part of the struct so you can
> then access it with ptrace/signals/core dumps.
>
>> If it would help I can post an alternate version of the patch for
>> discussion with the kittyhawk version.
>
> Sure.
>
Kittyhawk version can be seen here:
http://git.kernel.org/?p=3Dlinux/kernel/git/ericvh/bluegene.git;a=3Dcommitd=
iff;h=3D94bffe786324b9bd07187b11afd836e3ec362d95
>
> The most useful thing would be to see the instruction definition for
> STFPDX/LFPDX.
>
https://wiki.alcf.anl.gov/images/d/d9/PPC440_FP2_arch.pdf
>>
>> >> =3DA0/*
>> >> diff --git a/arch/powerpc/platforms/44x/Kconfig b/arch/powerpc/platfo=
rms=3D
>> /44x/
>> > Kconfig
>> >> index f485fc5f..24a515e 100644
>> >> --- a/arch/powerpc/platforms/44x/Kconfig
>> >> +++ b/arch/powerpc/platforms/44x/Kconfig
>> >> @@ -169,6 +169,15 @@ config YOSEMITE
>> >> =3DA0 =3DA0 =3DA0 help
>> >> =3DA0 =3DA0 =3DA0 =3DA0 This option enables support for the AMCC PPC4=
40EP evalua=3D
>> tion board.
>> >>
>> >> +config =3DA0 =3DA0 =3DA0 BGP
>> >
>> > Does this FPU feature have a specific name like double hammer? =3DA0I'=
d
>> > rather have the BGP defconfig depend on PPC_FPU_DOUBLE_HUMMER, or
>> > something like that...
>> >
>> >> + =3DA0 =3DA0 bool "Blue Gene/P"
>> >> + =3DA0 =3DA0 depends on 44x
>> >> + =3DA0 =3DA0 default n
>> >> + =3DA0 =3DA0 select PPC_FPU
>> >> + =3DA0 =3DA0 select PPC_DOUBLE_FPU
>> >
>> > ... in fact, it seem you are doing something like these here but you
>> > don't use PPC_DOUBLE_FPU anywhere?
>> >
>>
>> A fair point. =A0I'm fine with calling it DOUBLE_HUMMER, but I wasn't su=
re if
>> that was "too internal" of a name for the kernel. =A0Let me know and
>> I'll fix it up.
>
> What I'm mostly concerned about is disassociating it with a particular
> CPU.
>
> If it has an external name, then all the better.
>
Since it isn't available on other chips, shoudl it just be PPC_BGP_FPU
or PPC_BGP_DOUBLE_FPU?
-eric
next prev parent reply other threads:[~2011-05-19 21:55 UTC|newest]
Thread overview: 43+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-05-18 21:24 [PATCH 1/7] [RFC] Mainline BG/P platform support Eric Van Hensbergen
2011-05-18 21:24 ` [PATCH 2/7] [RFC] add bluegene entry to cputable Eric Van Hensbergen
2011-05-20 0:35 ` Benjamin Herrenschmidt
2011-05-20 1:08 ` Eric Van Hensbergen
2011-05-20 1:50 ` Benjamin Herrenschmidt
2011-05-18 21:24 ` [PATCH 3/7] [RFC] add support for BlueGene/P FPU Eric Van Hensbergen
2011-05-19 5:58 ` Michael Neuling
2011-05-19 13:53 ` Eric Van Hensbergen
2011-05-19 15:22 ` [bg-linux] " Kazutomo Yoshii
2011-05-19 21:36 ` Michael Neuling
2011-05-19 21:55 ` Eric Van Hensbergen [this message]
2011-05-19 23:16 ` Michael Neuling
2011-05-20 0:30 ` Eric Van Hensbergen
2011-05-20 0:43 ` Michael Neuling
2011-05-20 0:53 ` Benjamin Herrenschmidt
2011-05-20 0:52 ` Benjamin Herrenschmidt
2011-05-19 21:41 ` [PATCH 3/7] [RFC][V2] add support for BlueGene/P Double FPU Eric Van Hensbergen
2011-05-18 21:24 ` [PATCH 4/7] [RFC] enable L1_WRITETHROUGH mode for BG/P Eric Van Hensbergen
2011-05-19 10:43 ` Josh Boyer
2011-05-19 12:53 ` Eric Van Hensbergen
2011-05-19 21:42 ` [PATCH 4/7] [RFC][V2] enable BGP_L1_WRITETHROUGH " Eric Van Hensbergen
2011-05-20 1:01 ` [PATCH 4/7] [RFC] enable L1_WRITETHROUGH " Benjamin Herrenschmidt
2011-05-18 21:24 ` [PATCH 5/7] [RFC] force 32-byte aligned kmallocs Eric Van Hensbergen
2011-05-20 0:36 ` Benjamin Herrenschmidt
2011-05-20 0:47 ` Eric Van Hensbergen
2011-05-20 1:50 ` Benjamin Herrenschmidt
2011-05-20 1:32 ` [bg-linux] " Kazutomo Yoshii
2011-05-20 2:08 ` Benjamin Herrenschmidt
2011-05-20 2:13 ` Benjamin Herrenschmidt
2011-05-20 3:02 ` Kazutomo Yoshii
2011-05-20 3:13 ` Benjamin Herrenschmidt
2011-05-18 21:24 ` [PATCH 6/7] [RFC] enable early TLBs for BG/P Eric Van Hensbergen
2011-05-20 0:39 ` Benjamin Herrenschmidt
2011-05-20 1:21 ` Eric Van Hensbergen
2011-05-20 1:54 ` Benjamin Herrenschmidt
2011-05-20 3:38 ` [bg-linux] " Kazutomo Yoshii
2011-05-20 3:52 ` Benjamin Herrenschmidt
2011-05-20 13:01 ` Eric Van Hensbergen
2011-05-20 22:20 ` Benjamin Herrenschmidt
2011-05-18 21:24 ` [PATCH 7/7] [RFC] SMP support code Eric Van Hensbergen
2011-05-20 1:05 ` Benjamin Herrenschmidt
2011-05-19 11:01 ` [PATCH 1/7] [RFC] Mainline BG/P platform support Josh Boyer
2011-05-19 12:35 ` Eric Van Hensbergen
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