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Re: [Qemu-devel] [PATCH v5 1/6] target/alpha: remove tlb_flush from alph
From: |
Emilio G. Cota |
Subject: |
Re: [Qemu-devel] [PATCH v5 1/6] target/alpha: remove tlb_flush from alpha_cpu_initfn |
Date: |
Tue, 9 Oct 2018 14:20:53 -0400 |
User-agent: |
Mutt/1.9.4 (2018-02-28) |
On Tue, Oct 09, 2018 at 18:55:30 +0100, Peter Maydell wrote:
> On 9 October 2018 at 18:45, Emilio G. Cota <address@hidden> wrote:
(snip)
> > @@ -201,7 +201,6 @@ static void alpha_cpu_initfn(Object *obj)
> > CPUAlphaState *env = &cpu->env;
> >
> > cs->env_ptr = env;
> > - tlb_flush(cs);
> >
> > env->lock_addr = -1;
> > #if defined(CONFIG_USER_ONLY)
> > --
> > 2.17.1
>
> Definitely agreed that we don't want to tlb_flush in the
> target cpu initfn.
>
>
> What's the codepath by which tlb_flush gets called on
> cpu reset? I had a quick look but couldn't find it...
>From cpu.c:
static void cpu_common_reset(CPUState *cpu)
{
CPUClass *cc = CPU_GET_CLASS(cpu);
...
if (tcg_enabled()) {
cpu_tb_jmp_cache_clear(cpu);
tcg_flush_softmmu_tlb(cpu);
}
}
tcg_flush_softmmu_tlb is defined in translate-all.c:
/* This is a wrapper for common code that can not use CONFIG_SOFTMMU */
void tcg_flush_softmmu_tlb(CPUState *cs)
{
#ifdef CONFIG_SOFTMMU
tlb_flush(cs);
#endif
}
> (The other dubious-looking bit of flushing in the
> target/alpha code is the code that generates calls
> to tb_flush()... we have very few calls to tb_flush
> outside the 'core' code and I suspect they could all
> be avoided.)
If the comment below is accurate, seems fair enough.
tb_flush is only called from target/alpha through a helper,
generated by:
/* PALBR */
tcg_gen_st_i64(vb, cpu_env, offsetof(CPUAlphaState, palbr));
/* Changing the PAL base register implies un-chaining all of the TBs
that ended with a CALL_PAL. Since the base register usually only
changes during boot, flushing everything works well. */
gen_helper_tb_flush(cpu_env);
return DISAS_PC_STALE;
Thanks,
Emilio
[Qemu-devel] [PATCH v5 6/6] cputlb: read CPUTLBEntry.addr_write atomically, Emilio G. Cota, 2018/10/09
[Qemu-devel] [PATCH v5 2/6] target/unicore32: remove tlb_flush from uc32_init_fn, Emilio G. Cota, 2018/10/09
[Qemu-devel] [PATCH v5 5/6] cputlb: serialize tlb updates with env->tlb_lock, Emilio G. Cota, 2018/10/09
[Qemu-devel] [PATCH v5 3/6] exec: introduce tlb_init, Emilio G. Cota, 2018/10/09