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Re: [Qemu-devel] [PATCH v6 1/3] cputlb: do not evict empty entries to th
From: |
Alex Bennée |
Subject: |
Re: [Qemu-devel] [PATCH v6 1/3] cputlb: do not evict empty entries to the vtlb |
Date: |
Wed, 16 Jan 2019 10:32:08 +0000 |
User-agent: |
mu4e 1.1.0; emacs 26.1.91 |
Emilio G. Cota <address@hidden> writes:
> Currently we evict an entry to the victim TLB when it doesn't match
> the current address. But it could be that there's no match because
> the current entry is empty (i.e. all -1's, for instance via tlb_flush).
> Do not evict the entry to the vtlb in that case.
>
> This change will help us keep track of the TLB's use rate, which
> we'll use to implement a policy for dynamic TLB sizing.
>
> Reviewed-by: Alex Bennée <address@hidden>
> Reviewed-by: Richard Henderson <address@hidden>
> Signed-off-by: Emilio G. Cota <address@hidden>
> ---
> include/exec/cpu-all.h | 9 +++++++++
> accel/tcg/cputlb.c | 2 +-
> 2 files changed, 10 insertions(+), 1 deletion(-)
>
> diff --git a/include/exec/cpu-all.h b/include/exec/cpu-all.h
> index 117d2fbbca..e21140049b 100644
> --- a/include/exec/cpu-all.h
> +++ b/include/exec/cpu-all.h
> @@ -362,6 +362,15 @@ static inline bool tlb_hit(target_ulong tlb_addr,
> target_ulong addr)
> return tlb_hit_page(tlb_addr, addr & TARGET_PAGE_MASK);
> }
>
> +/**
> + * tlb_entry_is_empty - return true if the entry is not in use
> + * @te: pointer to CPUTLBEntry
> + */
> +static inline bool tlb_entry_is_empty(const CPUTLBEntry *te)
> +{
> + return te->addr_read == -1 && te->addr_write == -1 && te->addr_code ==
> -1;
> +}
> +
This breaks on a --disable-tcg build. I think the whole block needs to
be in a:
#if !defined(CONFIG_USER_ONLY) && defined(CONFIG_TCG)
now.
> void dump_exec_info(FILE *f, fprintf_function cpu_fprintf);
> void dump_opcount_info(FILE *f, fprintf_function cpu_fprintf);
> #endif /* !CONFIG_USER_ONLY */
> diff --git a/accel/tcg/cputlb.c b/accel/tcg/cputlb.c
> index af6bd8ccf9..5dc97212a9 100644
> --- a/accel/tcg/cputlb.c
> +++ b/accel/tcg/cputlb.c
> @@ -591,7 +591,7 @@ void tlb_set_page_with_attrs(CPUState *cpu, target_ulong
> vaddr,
> * Only evict the old entry to the victim tlb if it's for a
> * different page; otherwise just overwrite the stale data.
> */
> - if (!tlb_hit_page_anyprot(te, vaddr_page)) {
> + if (!tlb_hit_page_anyprot(te, vaddr_page) && !tlb_entry_is_empty(te)) {
> unsigned vidx = env->tlb_d[mmu_idx].vindex++ % CPU_VTLB_SIZE;
> CPUTLBEntry *tv = &env->tlb_v_table[mmu_idx][vidx];
--
Alex Bennée