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[Qemu-devel] Question about adding IBTC (Indirect Branch Translation Cac
From: |
陳韋任 |
Subject: |
[Qemu-devel] Question about adding IBTC (Indirect Branch Translation Cache) into QEMU |
Date: |
Wed, 10 Aug 2011 12:01:44 +0800 |
User-agent: |
Mutt/1.5.21 (2010-09-15) |
Hi, all
I want to add a binary tranlation optimization, called IBTC
(Indirect Branch Translation Cache) to QEMU. IBTC is a data
structure used to cache the mapping between guest IB (indirect
branch) and its corresponding translated code cache address.
If IBTC get a hit, then there is no need to jump back to QEMU,
next translated code cache can be excuted directly. An example
below.
=------------------- target-i386/translation.c -------------------=
static target_ulong disas_insn(CPUState *env, DisasContext *s, target_ulong
pc_start)
{
// Place IBTC lookup in the following cases
case 2: /* call Ev */
case 4: /* jmp Ev */
case 0xc2: /* ret im */
/*
* generate IBTC lookup TCG IR in the code cache while
* encounting indirect branch (ret im)
*/
if (s->cc_op != CC_OP_DYNAMIC)
gen_op_set_cc_op(s->cc_op);
TCGv_ptr ibtc_host_eip = tcg_temp_new_ptr();
gen_helper_lookup_ibtc(ibtc_host_eip, cpu_T[0]);
*gen_opc_ptr++ = INDEX_op_jmp;
*gen_opparam_ptr++ = GET_TCGV_PTR(ibtc_host_eip);
tcg_temp_free_ptr(ibtc_host_eip);
gen_eob(s);
break;
case 0xc3: /* ret */
}
=------------------- target-i386/translation.c -------------------=
IBTC works fine in the process (user) mode, but not in the system
mode. In process mode, since the IBTC allocated is big enough, I
don't need to invalidate an IBTC entry or flush the entire IBTC. I
suspect this is why IBTC doesn't work in the system mode. I spot a
few place to might be needed to call flush_ibtc() to flush the entire
IBTC, but I am not sure if there are the right place. Or I might miss
some place. The places I insert flush_ibtc are below,
-----
1. cpu-exec.c
int cpu_exec(CPUState *env1)
{
if (tb_invalidated_flag) {
next_tb = 0;
flush_ibtc(); // flush IBTC
tb_invalidated_flag = 0;
}
}
2. exec.c
TranslationBlock *tb_gen_code(CPUState *env,
target_ulong pc, target_ulong cs_base,
int flags, int cflags)
{
if (!tb) {
/* flush must be done */
tb_flush(env);
flush_ibtc(); // flush IBTC
/* cannot fail at this point */
tb = tb_alloc(pc);
/* Don't forget to invalidate previous TB info. */
tb_invalidated_flag = 1;
}
}
3. exec.c
void tb_phys_invalidate(TranslationBlock *tb, tb_page_addr_t page_addr)
{
tb_invalidated_flag = 1;
/* remove the TB from the hash list */
h = tb_jmp_cache_hash_func(tb->pc);
for(env = first_cpu; env != NULL; env = env->next_cpu) {
if (env->tb_jmp_cache[h] == tb)
env->tb_jmp_cache[h] = NULL;
}
flush_ibtc(); // flush IBTC
}
-----
Have I already considered all kind of situations? Or something else
I need to do to make IBTC work in system mode?
Thanks!
Regards,
chenwj
--
Wei-Ren Chen (陳韋任)
Computer Systems Lab, Institute of Information Science,
Academia Sinica, Taiwan (R.O.C.)
Tel:886-2-2788-3799 #1667
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