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Re: [Qemu-devel] [RFC] alpha qemu arithmetic exceptions
From: |
Al Viro |
Subject: |
Re: [Qemu-devel] [RFC] alpha qemu arithmetic exceptions |
Date: |
Tue, 8 Jul 2014 18:20:02 +0100 |
User-agent: |
Mutt/1.5.21 (2010-09-15) |
On Tue, Jul 08, 2014 at 05:33:16PM +0100, Peter Maydell wrote:
> > Incidentally, combination of --enable-gprof and (default) --enable-pie
> > won't build - it dies with ld(1) complaining about relocs in gcrt1.o.
>
> This sounds like a toolchain bug to me :-)
Debian stable/amd64, gcc 4.7.2, binutils 2.22. And google search finds
this, for example: http://osdir.com/ml/qemu-devel/2013-05/msg00710.html.
That one has gcc 4.4.3.
Anyway, adding --disable-pie to --enable-gprof gets it to build, but
as I said, gprof is no better than perf and oprofile - same problem.
Stats I quoted were from qemu-system-alpha booting debian/lenny (5.10) and
going through their kernel package build. I have perf report in front of
me right now; the top ones are
41.77% qemu-system-alp perf-24701.map [.] 0x7fbbee558930
11.78% qemu-system-alp qemu-system-alpha [.] cpu_alpha_exec
4.95% qemu-system-alp [vdso] [.] 0x7fffdd7ff8de
2.40% qemu-system-alp qemu-system-alpha [.] phys_page_find
1.49% qemu-system-alp qemu-system-alpha [.]
address_space_translate_internal
1.34% qemu-system-alp [kernel.kallsyms] [k] read_hpet
1.26% qemu-system-alp qemu-system-alpha [.] tlb_set_page
1.23% qemu-system-alp qemu-system-alpha [.] find_next_bit
1.04% qemu-system-alp qemu-system-alpha [.] get_page_addr_code
1.01% qemu-system-alp libpthread-2.13.so [.] pthread_mutex_lock
0.88% qemu-system-alp qemu-system-alpha [.] helper_cmpbge
0.80% qemu-system-alp libc-2.13.so [.] __memset_sse2
0.72% qemu-system-alp libpthread-2.13.so [.]
__pthread_mutex_unlock_usercnt
0.70% qemu-system-alp qemu-system-alpha [.] get_physical_address
0.69% qemu-system-alp qemu-system-alpha [.] address_space_translate
0.68% qemu-system-alp qemu-system-alpha [.] tcg_optimize
0.67% qemu-system-alp qemu-system-alpha [.] ldq_phys
0.63% qemu-system-alp qemu-system-alpha [.] qemu_get_ram_ptr
0.62% qemu-system-alp qemu-system-alpha [.] helper_le_ldq_mmu
0.57% qemu-system-alp qemu-system-alpha [.] memory_region_is_ram
and cpu_alpha_exec() spends most of the time in inlined tb_find_fast().
It might be worth checking the actual distribution of the hash of virt
address used by that sucker - I wonder if dividing its argument by 4
wouldn't improve the things, but I don't have stats on actual frequency
of conflicts, etc. In any case, the first lump (42%) seems to be tastier ;-)
There are all kinds of microoptimizations possible (e.g. helper_cmpbge() could
be done by a couple of MMX insns on amd64 host[1]), but it would be nice to
have some details on what we spend the time on in tcg output...
[1] The reason why helper_cmpbge() shows up is that string functions on alpha
use that insn a lot; it _might_ be worth optimizing.
- Re: [Qemu-devel] [RFC] alpha qemu arithmetic exceptions, (continued)
- Re: [Qemu-devel] [RFC] alpha qemu arithmetic exceptions, Al Viro, 2014/07/07
- Re: [Qemu-devel] [RFC] alpha qemu arithmetic exceptions, Richard Henderson, 2014/07/07
- Re: [Qemu-devel] [RFC] alpha qemu arithmetic exceptions, Al Viro, 2014/07/08
- Re: [Qemu-devel] [RFC] alpha qemu arithmetic exceptions, Richard Henderson, 2014/07/08
- Re: [Qemu-devel] [RFC] alpha qemu arithmetic exceptions, Al Viro, 2014/07/08
- Re: [Qemu-devel] [RFC] alpha qemu arithmetic exceptions, Al Viro, 2014/07/08
- Re: [Qemu-devel] [RFC] alpha qemu arithmetic exceptions, Peter Maydell, 2014/07/08
- Re: [Qemu-devel] [RFC] alpha qemu arithmetic exceptions, Richard Henderson, 2014/07/08
- Re: [Qemu-devel] [RFC] alpha qemu arithmetic exceptions, Al Viro, 2014/07/08
- Re: [Qemu-devel] [RFC] alpha qemu arithmetic exceptions, Peter Maydell, 2014/07/08
- Re: [Qemu-devel] [RFC] alpha qemu arithmetic exceptions,
Al Viro <=
- Re: [Qemu-devel] [RFC] alpha qemu arithmetic exceptions, Peter Maydell, 2014/07/08
- Re: [Qemu-devel] [RFC] alpha qemu arithmetic exceptions, Al Viro, 2014/07/10
- Re: [Qemu-devel] [RFC] alpha qemu arithmetic exceptions, Alex Bennée, 2014/07/10
- Re: [Qemu-devel] [RFC] alpha qemu arithmetic exceptions, Alex Bennée, 2014/07/09
- Re: [Qemu-devel] [RFC] alpha qemu arithmetic exceptions, Richard Henderson, 2014/07/08
- Re: [Qemu-devel] [RFC] alpha qemu arithmetic exceptions, Al Viro, 2014/07/08
- Re: [Qemu-devel] [RFC] alpha qemu arithmetic exceptions, Richard Henderson, 2014/07/08
- Re: [Qemu-devel] [RFC] alpha qemu arithmetic exceptions, Al Viro, 2014/07/08
- Re: [Qemu-devel] [RFC] alpha qemu arithmetic exceptions, Richard Henderson, 2014/07/09
- Re: [Qemu-devel] [RFC] alpha qemu arithmetic exceptions, Al Viro, 2014/07/09