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Re: [Qemu-devel] Debian 7.8.0 SPARC64 on qemu - anything i can do to spe
From: |
Aurelien Jarno |
Subject: |
Re: [Qemu-devel] Debian 7.8.0 SPARC64 on qemu - anything i can do to speedup the emulation? |
Date: |
Wed, 19 Aug 2015 13:00:10 +0200 |
User-agent: |
Mutt/1.5.23 (2014-03-12) |
On 2015-08-19 12:41, Artyom Tarasenko wrote:
> Hi Richard,
>
> On Tue, Aug 18, 2015 at 7:55 PM, Richard Henderson <address@hidden> wrote:
> > On 08/18/2015 02:24 AM, Artyom Tarasenko wrote:
> >> The unoptimized case is a sequence of multiple cmp and branch
> >> operations (likely created by a "case" statement in the original
> >> source code), especially where cmp is in a delay slot of a branch
> >> instruction.
> >
> > Interesting.
> >
> >> I wonder whether we always have to finish a TB on a conditional jump.
> >> Maybe it would make sense to translate further if a destination of a
> >> jump is not too far from dc->pc? The definition of "not too far" is
> >> indeed tricky.
> >
> > We can only handle two chained exits from a TB. If we continue past
> > a conditional branch, we may well encounter a second conditional branch,
> > which
> > would leave us with three different exits from the TB.
> >
> > Something that may be interesting to play with, however, is to change the TB
> > with which the insn in a delay slot is connected.
> >
> > For instance, we currently spend some amount of effort computing and saving
> > the
> > branch condition, so that we can then execute the delay slot, and afterwards
> > use the saved branch condition to perform the branch.
> >
> > Another way of doing this is to immediately branch, exiting the TB. But we
> > set
> > up PC+NPC for the next TB such that the delay slot is the first insn that is
> > executed within the next TB. In that way, the compare in the delay slot
> > that
> > you mention *is* in the same TB as the branch that uses it, allowing
> > the case to be optimized.
> >
> > This could wind up creating more TBs than the current solution, so it's not
> > clear that it would be a win. One can mitigate that somewhat by noticing
> > the
> > case where the delay slot is a nop. I do think it's worth an experiment.
>
> So it is possible to make a TB with non sequential instructions?
> The instruction in the delay slot would be located most likely
> elsewhere than the following instructions.
>
> But I think I've been chasing a red herring. I see those helpers in
> perf top when running sysbench, but not when running g++ (and at the
> end g++ is much more relevant benchmark for me):
>
>
> Samples: 83K of event 'cpu-clock', Event count (approx.): 15333243164,
> Thread: qemu-system-spa(2743)
> 27.10% [kernel] [k] retint_signal
> 12.66% qemu-system-sparc64 [.] tcg_optimize
> 9.18% [vdso] [.] 0x0000000000000998
> 8.39% [kernel] [k] _raw_spin_unlock_irqrestore
> 4.76% qemu-system-sparc64 [.] tcg_liveness_analysis
> 3.89% qemu-system-sparc64 [.] tcg_reg_alloc_op
> 2.80% qemu-system-sparc64 [.] tcg_out_opc
> 2.45% qemu-system-sparc64 [.] get_physical_address_data
> 1.86% [kernel] [k] native_read_tsc
> 1.62% qemu-system-sparc64 [.] tlb_flush_page
> 1.55% qemu-system-sparc64 [.] tcg_out_modrm_sib_offset.constprop.42
> 1.45% [unknown] [.] 0x00000000451c5cae
> 1.43% qemu-system-sparc64 [.] gen_intermediate_code_pc
> 1.39% qemu-system-sparc64 [.] tcg_temp_new_internal_i64
> 1.24% qemu-system-sparc64 [.] tb_flush_jmp_cache
> 1.11% qemu-system-sparc64 [.] disas_sparc_insn
> 1.08% qemu-system-sparc64 [.] tcg_out_modrm
> 0.97% qemu-system-sparc64 [.] tcg_reg_alloc_start
> 0.77% qemu-system-sparc64 [.] cpu_sparc_exec
> 0.73% qemu-system-sparc64 [.] replace_tlb_1bit_lru.isra.3
> 0.72% qemu-system-sparc64 [.] tcg_gen_code_search_pc
> 0.72% qemu-system-sparc64 [.] tcg_opt_gen_mov
> 0.70% qemu-system-sparc64 [.] reset_temp
>
> I'm not sure why I still see kernel functions when I zoom into qemu
> thread. Is this qemu signal handling?
> And then it would be interesting to know where in this listing is the
> generated code. Is it [vdso], [unknown] or is it hidden behind
> retint_signal?
>
> Ironically a good optimization target seems to be the tcg_optimize
> function. If I zoom I see it spends most of the time in
> reset_all_temps.
>
> Any suggestions how to improve it?
>
Try this patch:
http://lists.nongnu.org/archive/html/qemu-devel/2015-08/msg02042.html
Aurelien
--
Aurelien Jarno GPG: 4096R/1DDD8C9B
address@hidden http://www.aurel32.net
- Re: [Qemu-devel] Debian 7.8.0 SPARC64 on qemu - anything i can do to speedup the emulation?, Mark Cave-Ayland, 2015/08/02
- Re: [Qemu-devel] Debian 7.8.0 SPARC64 on qemu - anything i can do to speedup the emulation?, Dennis Luehring, 2015/08/03
- Re: [Qemu-devel] Debian 7.8.0 SPARC64 on qemu - anything i can do to speedup the emulation?, Artyom Tarasenko, 2015/08/03
- Re: [Qemu-devel] Debian 7.8.0 SPARC64 on qemu - anything i can do to speedup the emulation?, Aurelien Jarno, 2015/08/03
- Re: [Qemu-devel] Debian 7.8.0 SPARC64 on qemu - anything i can do to speedup the emulation?, Artyom Tarasenko, 2015/08/18
- Re: [Qemu-devel] Debian 7.8.0 SPARC64 on qemu - anything i can do to speedup the emulation?, Richard Henderson, 2015/08/18
- Re: [Qemu-devel] Debian 7.8.0 SPARC64 on qemu - anything i can do to speedup the emulation?, Artyom Tarasenko, 2015/08/19
- Re: [Qemu-devel] Debian 7.8.0 SPARC64 on qemu - anything i can do to speedup the emulation?,
Aurelien Jarno <=
- Re: [Qemu-devel] Debian 7.8.0 SPARC64 on qemu - anything i can do to speedup the emulation?, Artyom Tarasenko, 2015/08/19
- Re: [Qemu-devel] Debian 7.8.0 SPARC64 on qemu - anything i can do to speedup the emulation?, Richard Henderson, 2015/08/20
- Re: [Qemu-devel] Debian 7.8.0 SPARC64 on qemu - anything i can do to speedup the emulation?, Dennis Luehring, 2015/08/21
- Re: [Qemu-devel] Debian 7.8.0 SPARC64 on qemu - anything i can do to speedup the emulation?, Richard Henderson, 2015/08/21
- Re: [Qemu-devel] Debian 7.8.0 SPARC64 on qemu - anything i can do to speedup the emulation?, Dennis Luehring, 2015/08/21
- Re: [Qemu-devel] Debian 7.8.0 SPARC64 on qemu - anything i can do to speedup the emulation?, Richard Henderson, 2015/08/21
- Re: [Qemu-devel] Debian 7.8.0 SPARC64 on qemu - anything i can do to speedup the emulation?, Aurelien Jarno, 2015/08/21
- Re: [Qemu-devel] Debian 7.8.0 SPARC64 on qemu - anything i can do to speedup the emulation?, Dennis Luehring, 2015/08/21
- Re: [Qemu-devel] Debian 7.8.0 SPARC64 on qemu - anything i can do to speedup the emulation?, Artyom Tarasenko, 2015/08/22
- Re: [Qemu-devel] Debian 7.8.0 SPARC64 on qemu - anything i can do to speedup the emulation?, Dennis Luehring, 2015/08/22