From: tony@atomide•com (Tony Lindgren)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH 1/2] arm: Replace CONFIG_HAS_TLS_REG with HWCAP_TLS and check for it on V6
Date: Tue, 29 Jun 2010 17:18:36 +0300 [thread overview]
Message-ID: <20100629141836.GM2822@atomide.com> (raw)
In-Reply-To: <20100623133636.GC7058@shareable.org>
* Jamie Lokier <jamie@shareable•org> [100623 16:30]:
> Tony Lindgren wrote:
> > * Jamie Lokier <jamie@shareable•org> [100622 19:54]:
> > > Tony Lindgren wrote:
> > > > __kuser_get_tls: @ 0xffff0fe0
> > > > -
> > > > -#if !defined(CONFIG_HAS_TLS_REG) && !defined(CONFIG_TLS_REG_EMUL)
> > > > - ldr r0, [pc, #(16 - 8)] @ TLS stored at 0xffff0ff0
> > > > -#else
> > > > - mrc p15, 0, r0, c13, c0, 3 @ read TLS register
> > > > -#endif
> > > > + ldr r0, [pc, #(20 - 8)] @ software TLS set in 0xffff0ff4?
> > > > + cmp r0, #0 @ hardware TLS if flag not set
> > > > + mrceq p15, 0, r0, c13, c0, 3 @ read hardware TLS register
> > > > + ldrne r0, [pc, #(12 - 8)] @ software TLS val at 0xffff0ff8
> > > > usr_ret lr
> > > > -
> > > > - .rep 5
> > > > - .word 0 @ pad up to __kuser_helper_version
> > > > - .endr
> > > > + .word 0 @ non-zero for software TLS
> > > > + .word 0 @ software TLS value
> > >
> > > It'd be nice not to waste instructions checking for HWCAP_TLS on archs
> > > which definitely don't have it. I guess it doesn't matter elsewhere;
> > > I'd expect this to be a warm path for some programs making extensive
> > > use of TLS (I haven't measured though).
> >
> > OK, but let's try to figure out a way that does not add more ifdef else
> > code as that makes it harder to build support for multiple ARM cores.
> >
> > > As it's only a single instruction, and the code is in a writable page
> > > already (copied at init), how about just patching the instruction
> > > when ELF_HWCAP is set?
> >
> > Yeah that can be done for __kuser_get_tls if it's always writable.
> > But __switch_to is trickier because of the CONFIG_MMU ifdefs there.
>
> __kuser_get_tls must be writable in kernels where !HAS_TLS_REG is
> supported, because the TLS value is written to the same page.
>
> I was thinking of changing *only* __kuser_get_tls, by the way. Out of
> all the different places, that's the only one I'd expect to be a hot
> path in some TLS-using programs.
OK. Sorry for the delay again. Here's an updated version that sets
__kuser_get_tls instruction dynamically. Does this do what you were
thinking, or did I miss something?
Also, can we detect somehow the hardware that uses CONFIG_TLS_REG_EMUL?
Might be possible to remove that Kconfig option too later on..
Regards,
Tony
-------------- next part --------------
A non-text attachment was scrubbed...
Name: arm-tls-v3.patch
Type: text/x-diff
Size: 7349 bytes
Desc: not available
URL: <http://lists.infradead.org/pipermail/linux-arm-kernel/attachments/20100629/99ddda56/attachment.bin>
next prev parent reply other threads:[~2010-06-29 14:18 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-06-21 13:51 [PATCH 0/2] Make ARMv6 behave with TLS, VFPv3, and NEON Tony Lindgren
2010-06-21 13:51 ` [PATCH 1/2] arm: Replace CONFIG_HAS_TLS_REG with HWCAP_TLS and check for it on V6 Tony Lindgren
2010-06-22 9:28 ` Tony Lindgren
2010-06-22 17:00 ` Jamie Lokier
2010-06-23 7:39 ` Tony Lindgren
2010-06-23 8:12 ` Russell King - ARM Linux
2010-06-23 9:28 ` Tony Lindgren
2010-06-23 9:32 ` Russell King - ARM Linux
2010-06-23 13:28 ` Jamie Lokier
2010-06-23 13:36 ` Jamie Lokier
2010-06-23 14:19 ` Nicolas Pitre
2010-06-24 0:28 ` Jamie Lokier
2010-06-29 14:18 ` Tony Lindgren [this message]
2010-06-29 19:20 ` Nicolas Pitre
2010-06-30 11:08 ` Tony Lindgren
2010-06-30 13:17 ` Tony Lindgren
2010-06-30 14:42 ` Nicolas Pitre
2010-07-01 9:25 ` Tony Lindgren
2010-07-01 17:40 ` Jamie Lokier
2010-07-02 2:37 ` Nicolas Pitre
2010-07-02 10:37 ` Tony Lindgren
2010-07-05 13:55 ` Tony Lindgren
2011-04-08 3:39 ` Li Li
2011-04-08 13:19 ` Nicolas Pitre
2011-04-08 13:35 ` Li Li
2011-04-08 14:35 ` Jamie Lokier
2011-04-08 14:40 ` Li Li
2010-06-21 13:51 ` [PATCH 2/2] arm: Make VFPv3 usable on ARMv6 Tony Lindgren
2010-06-22 12:59 ` Catalin Marinas
2010-06-22 13:20 ` Tony Lindgren
2010-06-23 7:57 ` Tony Lindgren
2010-06-25 13:50 ` Catalin Marinas
2010-07-01 12:42 ` Tony Lindgren
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20100629141836.GM2822@atomide.com \
--to=tony@atomide$(echo .)com \
--cc=linux-arm-kernel@lists$(echo .)infradead.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox