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Re: [PATCH]: R10000 Needs LL/SC Workaround in Glibc
- From: Ralf Baechle <ralf at linux-mips dot org>
- To: Kumba <kumba at gentoo dot org>
- Cc: libc-ports at sources dot redhat dot com, Daniel Jacobowitz <drow at false dot org>, Linux MIPS List <linux-mips at linux-mips dot org>
- Date: Sat, 1 Nov 2008 11:26:43 +0000
- Subject: Re: [PATCH]: R10000 Needs LL/SC Workaround in Glibc
- References: <490A912A.8030901@gentoo.org>
On Fri, Oct 31, 2008 at 01:01:30AM -0400, Kumba wrote:
> +#ifndef (_MIPS_ARCH_R10000)
> +#define R10K_BEQZ_INSN "beqz %1,1b\n"
> +#else
> +#define R10K_BEQZ_INSN "beqzl %1,1b\n"
> +#endif
In the kernel we have very good knowledge about what types of processors
are being used for what configuration; much less in userland and the code
as suggested by you would result in a silent failure on affected R10000
machines if version built not for the R10000 was being used - iow no
improvment over what we have right now. So for userland I'd prefer to
o MIPS I builds: use the some 28 nops.
o Builds for MIPS II or better: always use the branch likely
o A runtime test would have to be implemented pessimisticall because it
would have to rely on /proc being mounted which isn't available early in
the boot process. It's probably going to add more overhead than it
saves anyway.
There is a price for using branch likely - but not that high. In the grand
picture it'll almost certainly vanish in the benchmarking noise.
Ralf